mod.rs - source (original) (raw)
std/io/
mod.rs
1//! Traits, helpers, and type definitions for core I/O functionality.
2//!
3//! The `std::io` module contains a number of common things you'll need
4//! when doing input and output. The most core part of this module is
5//! the [`Read`] and [`Write`] traits, which provide the
6//! most general interface for reading and writing input and output.
7//!
8//! ## Read and Write
9//!
10//! Because they are traits, [`Read`] and [`Write`] are implemented by a number
11//! of other types, and you can implement them for your types too. As such,
12//! you'll see a few different types of I/O throughout the documentation in
13//! this module: [`File`]s, [`TcpStream`]s, and sometimes even [`Vec<T>`]s. For
14//! example, [`Read`] adds a [`read`][`Read::read`] method, which we can use on
15//! [`File`]s:
16//!
17//! ```no_run
18//! use std::io;
19//! use std::io::prelude::*;
20//! use std::fs::File;
21//!
22//! fn main() -> io::Result<()> {
23//! let mut f = File::open("foo.txt")?;
24//! let mut buffer = [0; 10];
25//!
26//! // read up to 10 bytes
27//! let n = f.read(&mut buffer)?;
28//!
29//! println!("The bytes: {:?}", &buffer[..n]);
30//! Ok(())
31//! }
32//! ```
33//!
34//! [`Read`] and [`Write`] are so important, implementors of the two traits have a
35//! nickname: readers and writers. So you'll sometimes see 'a reader' instead
36//! of 'a type that implements the [`Read`] trait'. Much easier!
37//!
38//! ## Seek and BufRead
39//!
40//! Beyond that, there are two important traits that are provided: [`Seek`]
41//! and [`BufRead`]. Both of these build on top of a reader to control
42//! how the reading happens. [`Seek`] lets you control where the next byte is
43//! coming from:
44//!
45//! ```no_run
46//! use std::io;
47//! use std::io::prelude::*;
48//! use std::io::SeekFrom;
49//! use std::fs::File;
50//!
51//! fn main() -> io::Result<()> {
52//! let mut f = File::open("foo.txt")?;
53//! let mut buffer = [0; 10];
54//!
55//! // skip to the last 10 bytes of the file
56//! f.seek(SeekFrom::End(-10))?;
57//!
58//! // read up to 10 bytes
59//! let n = f.read(&mut buffer)?;
60//!
61//! println!("The bytes: {:?}", &buffer[..n]);
62//! Ok(())
63//! }
64//! ```
65//!
66//! [`BufRead`] uses an internal buffer to provide a number of other ways to read, but
67//! to show it off, we'll need to talk about buffers in general. Keep reading!
68//!
69//! ## BufReader and BufWriter
70//!
71//! Byte-based interfaces are unwieldy and can be inefficient, as we'd need to be
72//! making near-constant calls to the operating system. To help with this,
73//! `std::io` comes with two structs, [`BufReader`] and [`BufWriter`], which wrap
74//! readers and writers. The wrapper uses a buffer, reducing the number of
75//! calls and providing nicer methods for accessing exactly what you want.
76//!
77//! For example, [`BufReader`] works with the [`BufRead`] trait to add extra
78//! methods to any reader:
79//!
80//! ```no_run
81//! use std::io;
82//! use std::io::prelude::*;
83//! use std::io::BufReader;
84//! use std::fs::File;
85//!
86//! fn main() -> io::Result<()> {
87//! let f = File::open("foo.txt")?;
88//! let mut reader = BufReader::new(f);
89//! let mut buffer = String::new();
90//!
91//! // read a line into buffer
92//! reader.read_line(&mut buffer)?;
93//!
94//! println!("{buffer}");
95//! Ok(())
96//! }
97//! ```
98//!
99//! [`BufWriter`] doesn't add any new ways of writing; it just buffers every call
100//! to [`write`][`Write::write`]:
101//!
102//! ```no_run
103//! use std::io;
104//! use std::io::prelude::*;
105//! use std::io::BufWriter;
106//! use std::fs::File;
107//!
108//! fn main() -> io::Result<()> {
109//! let f = File::create("foo.txt")?;
110//! {
111//! let mut writer = BufWriter::new(f);
112//!
113//! // write a byte to the buffer
114//! writer.write(&[42])?;
115//!
116//! } // the buffer is flushed once writer goes out of scope
117//!
118//! Ok(())
119//! }
120//! ```
121//!
122//! ## Standard input and output
123//!
124//! A very common source of input is standard input:
125//!
126//! ```no_run
127//! use std::io;
128//!
129//! fn main() -> io::Result<()> {
130//! let mut input = String::new();
131//!
132//! io::stdin().read_line(&mut input)?;
133//!
134//! println!("You typed: {}", input.trim());
135//! Ok(())
136//! }
137//! ```
138//!
139//! Note that you cannot use the [`?` operator] in functions that do not return
140//! a [`Result<T, E>`][`Result`]. Instead, you can call [`.unwrap()`]
141//! or `match` on the return value to catch any possible errors:
142//!
143//! ```no_run
144//! use std::io;
145//!
146//! let mut input = String::new();
147//!
148//! io::stdin().read_line(&mut input).unwrap();
149//! ```
150//!
151//! And a very common source of output is standard output:
152//!
153//! ```no_run
154//! use std::io;
155//! use std::io::prelude::*;
156//!
157//! fn main() -> io::Result<()> {
158//! io::stdout().write(&[42])?;
159//! Ok(())
160//! }
161//! ```
162//!
163//! Of course, using [`io::stdout`] directly is less common than something like
164//! [`println!`].
165//!
166//! ## Iterator types
167//!
168//! A large number of the structures provided by `std::io` are for various
169//! ways of iterating over I/O. For example, [`Lines`] is used to split over
170//! lines:
171//!
172//! ```no_run
173//! use std::io;
174//! use std::io::prelude::*;
175//! use std::io::BufReader;
176//! use std::fs::File;
177//!
178//! fn main() -> io::Result<()> {
179//! let f = File::open("foo.txt")?;
180//! let reader = BufReader::new(f);
181//!
182//! for line in reader.lines() {
183//! println!("{}", line?);
184//! }
185//! Ok(())
186//! }
187//! ```
188//!
189//! ## Functions
190//!
191//! There are a number of [functions][functions-list] that offer access to various
192//! features. For example, we can use three of these functions to copy everything
193//! from standard input to standard output:
194//!
195//! ```no_run
196//! use std::io;
197//!
198//! fn main() -> io::Result<()> {
199//! io::copy(&mut io::stdin(), &mut io::stdout())?;
200//! Ok(())
201//! }
202//! ```
203//!
204//! [functions-list]: #functions-1
205//!
206//! ## io::Result
207//!
208//! Last, but certainly not least, is [`io::Result`]. This type is used
209//! as the return type of many `std::io` functions that can cause an error, and
210//! can be returned from your own functions as well. Many of the examples in this
211//! module use the [`?` operator]:
212//!
213//! ```
214//! use std::io;
215//!
216//! fn read_input() -> io::Result<()> {
217//! let mut input = String::new();
218//!
219//! io::stdin().read_line(&mut input)?;
220//!
221//! println!("You typed: {}", input.trim());
222//!
223//! Ok(())
224//! }
225//! ```
226//!
227//! The return type of `read_input()`, [`io::Result<()>`][`io::Result`], is a very
228//! common type for functions which don't have a 'real' return value, but do want to
229//! return errors if they happen. In this case, the only purpose of this function is
230//! to read the line and print it, so we use `()`.
231//!
232//! ## Platform-specific behavior
233//!
234//! Many I/O functions throughout the standard library are documented to indicate
235//! what various library or syscalls they are delegated to. This is done to help
236//! applications both understand what's happening under the hood as well as investigate
237//! any possibly unclear semantics. Note, however, that this is informative, not a binding
238//! contract. The implementation of many of these functions are subject to change over
239//! time and may call fewer or more syscalls/library functions.
240//!
241//! ## I/O Safety
242//!
243//! Rust follows an I/O safety discipline that is comparable to its memory safety discipline. This
244//! means that file descriptors can be *exclusively owned*. (Here, "file descriptor" is meant to
245//! subsume similar concepts that exist across a wide range of operating systems even if they might
246//! use a different name, such as "handle".) An exclusively owned file descriptor is one that no
247//! other code is allowed to access in any way, but the owner is allowed to access and even close
248//! it any time. A type that owns its file descriptor should usually close it in its `drop`
249//! function. Types like [`File`] own their file descriptor. Similarly, file descriptors
250//! can be *borrowed*, granting the temporary right to perform operations on this file descriptor.
251//! This indicates that the file descriptor will not be closed for the lifetime of the borrow, but
252//! it does *not* imply any right to close this file descriptor, since it will likely be owned by
253//! someone else.
254//!
255//! The platform-specific parts of the Rust standard library expose types that reflect these
256//! concepts, see [`os::unix`] and [`os::windows`].
257//!
258//! To uphold I/O safety, it is crucial that no code acts on file descriptors it does not own or
259//! borrow, and no code closes file descriptors it does not own. In other words, a safe function
260//! that takes a regular integer, treats it as a file descriptor, and acts on it, is *unsound*.
261//!
262//! Not upholding I/O safety and acting on a file descriptor without proof of ownership can lead to
263//! misbehavior and even Undefined Behavior in code that relies on ownership of its file
264//! descriptors: a closed file descriptor could be re-allocated, so the original owner of that file
265//! descriptor is now working on the wrong file. Some code might even rely on fully encapsulating
266//! its file descriptors with no operations being performed by any other part of the program.
267//!
268//! Note that exclusive ownership of a file descriptor does *not* imply exclusive ownership of the
269//! underlying kernel object that the file descriptor references (also called "open file description" on
270//! some operating systems). File descriptors basically work like [`Arc`]: when you receive an owned
271//! file descriptor, you cannot know whether there are any other file descriptors that reference the
272//! same kernel object. However, when you create a new kernel object, you know that you are holding
273//! the only reference to it. Just be careful not to lend it to anyone, since they can obtain a
274//! clone and then you can no longer know what the reference count is! In that sense, [`OwnedFd`] is
275//! like `Arc` and [`BorrowedFd<'a>`] is like `&'a Arc` (and similar for the Windows types). In
276//! particular, given a `BorrowedFd<'a>`, you are not allowed to close the file descriptor -- just
277//! like how, given a `&'a Arc`, you are not allowed to decrement the reference count and
278//! potentially free the underlying object. There is no equivalent to `Box` for file descriptors in
279//! the standard library (that would be a type that guarantees that the reference count is `1`),
280//! however, it would be possible for a crate to define a type with those semantics.
281//!
282//! [`File`]: crate::fs::File
283//! [`TcpStream`]: crate:🥅:TcpStream
284//! [`io::stdout`]: stdout
285//! [`io::Result`]: self::Result
286//! [`?` operator]: ../../book/appendix-02-operators.html
287//! [`Result`]: crate::result::Result
288//! [`.unwrap()`]: crate::result::Result::unwrap
289//! [`os::unix`]: ../os/unix/io/index.html
290//! [`os::windows`]: ../os/windows/io/index.html
291//! [`OwnedFd`]: ../os/fd/struct.OwnedFd.html
292//! [`BorrowedFd<'a>`]: ../os/fd/struct.BorrowedFd.html
293//! [`Arc`]: crate::sync::Arc
294
295#![stable(feature = "rust1", since = "1.0.0")]
296
297#[cfg(test)]
298mod tests;
299
300#[unstable(feature = "read_buf", issue = "78485")]
301pub use core::io::{BorrowedBuf, BorrowedCursor};
302use core::slice::memchr;
303
304#[stable(feature = "bufwriter_into_parts", since = "1.56.0")]
305pub use self::buffered::WriterPanicked;
306#[unstable(feature = "raw_os_error_ty", issue = "107792")]
307pub use self::error::RawOsError;
308#[doc(hidden)]
309#[unstable(feature = "io_const_error_internals", issue = "none")]
310pub use self::error::SimpleMessage;
311#[unstable(feature = "io_const_error", issue = "133448")]
312pub use self::error::const_error;
313#[stable(feature = "anonymous_pipe", since = "1.87.0")]
314pub use self::pipe::{PipeReader, PipeWriter, pipe};
315#[stable(feature = "is_terminal", since = "1.70.0")]
316pub use self::stdio::IsTerminal;
317pub(crate) use self::stdio::attempt_print_to_stderr;
318#[unstable(feature = "print_internals", issue = "none")]
319#[doc(hidden)]
320pub use self::stdio::{_eprint, _print};
321#[unstable(feature = "internal_output_capture", issue = "none")]
322#[doc(no_inline, hidden)]
323pub use self::stdio::{set_output_capture, try_set_output_capture};
324#[stable(feature = "rust1", since = "1.0.0")]
325pub use self::{
326 buffered::{BufReader, BufWriter, IntoInnerError, LineWriter},
327 copy::copy,
328 cursor::Cursor,
329 error::{Error, ErrorKind, Result},
330 stdio::{Stderr, StderrLock, Stdin, StdinLock, Stdout, StdoutLock, stderr, stdin, stdout},
331 util::{Empty, Repeat, Sink, empty, repeat, sink},
332};
333use crate::mem::take;
334use crate::ops::{Deref, DerefMut};
335use crate::{cmp, fmt, slice, str, sys};
336
337mod buffered;
338pub(crate) mod copy;
339mod cursor;
340mod error;
341mod impls;
342mod pipe;
343pub mod prelude;
344mod stdio;
345mod util;
346
347const DEFAULT_BUF_SIZE: usize = crate::sys::io::DEFAULT_BUF_SIZE;
348
349pub(crate) use stdio::cleanup;
350
351struct Guard<'a> {
352 buf: &'a mut Vec<u8>,
353 len: usize,
354}
355
356impl Drop for Guard<'_> {
357 fn drop(&mut self) {
358 unsafe {
359 self.buf.set_len(self.len);
360 }
361 }
362}
363
364// Several `read_to_string` and `read_line` methods in the standard library will
365// append data into a `String` buffer, but we need to be pretty careful when
366// doing this. The implementation will just call `.as_mut_vec()` and then
367// delegate to a byte-oriented reading method, but we must ensure that when
368// returning we never leave `buf` in a state such that it contains invalid UTF-8
369// in its bounds.
370//
371// To this end, we use an RAII guard (to protect against panics) which updates
372// the length of the string when it is dropped. This guard initially truncates
373// the string to the prior length and only after we've validated that the
374// new contents are valid UTF-8 do we allow it to set a longer length.
375//
376// The unsafety in this function is twofold:
377//
378// 1. We're looking at the raw bytes of `buf`, so we take on the burden of UTF-8
379// checks.
380// 2. We're passing a raw buffer to the function `f`, and it is expected that
381// the function only *appends* bytes to the buffer. We'll get undefined
382// behavior if existing bytes are overwritten to have non-UTF-8 data.
383pub(crate) unsafe fn append_to_string<F>(buf: &mut String, f: F) -> Result<usize>
384where
385 F: FnOnce(&mut Vec<u8>) -> Result<usize>,
386{
387 let mut g = Guard { len: buf.len(), buf: unsafe { buf.as_mut_vec() } };
388 let ret = f(g.buf);
389
390 // SAFETY: the caller promises to only append data to `buf`
391 let appended = unsafe { g.buf.get_unchecked(g.len..) };
392 if str::from_utf8(appended).is_err() {
393 ret.and_then(|_| Err(Error::INVALID_UTF8))
394 } else {
395 g.len = g.buf.len();
396 ret
397 }
398}
399
400// Here we must serve many masters with conflicting goals:
401//
402// - avoid allocating unless necessary
403// - avoid overallocating if we know the exact size (#89165)
404// - avoid passing large buffers to readers that always initialize the free capacity if they perform short reads (#23815, #23820)
405// - pass large buffers to readers that do not initialize the spare capacity. this can amortize per-call overheads
406// - and finally pass not-too-small and not-too-large buffers to Windows read APIs because they manage to suffer from both problems
407// at the same time, i.e. small reads suffer from syscall overhead, all reads incur costs proportional to buffer size (#110650)
408//
409pub(crate) fn default_read_to_end<R: Read + ?Sized>(
410 r: &mut R,
411 buf: &mut Vec<u8>,
412 size_hint: Option<usize>,
413) -> Result<usize> {
414 let start_len = buf.len();
415 let start_cap = buf.capacity();
416 // Optionally limit the maximum bytes read on each iteration.
417 // This adds an arbitrary fiddle factor to allow for more data than we expect.
418 let mut max_read_size = size_hint
419 .and_then(|s| s.checked_add(1024)?.checked_next_multiple_of(DEFAULT_BUF_SIZE))
420 .unwrap_or(DEFAULT_BUF_SIZE);
421
422 let mut initialized = 0; // Extra initialized bytes from previous loop iteration
423
424 const PROBE_SIZE: usize = 32;
425
426 fn small_probe_read<R: Read + ?Sized>(r: &mut R, buf: &mut Vec<u8>) -> Result<usize> {
427 let mut probe = [0u8; PROBE_SIZE];
428
429 loop {
430 match r.read(&mut probe) {
431 Ok(n) => {
432 // there is no way to recover from allocation failure here
433 // because the data has already been read.
434 buf.extend_from_slice(&probe[..n]);
435 return Ok(n);
436 }
437 Err(ref e) if e.is_interrupted() => continue,
438 Err(e) => return Err(e),
439 }
440 }
441 }
442
443 // avoid inflating empty/small vecs before we have determined that there's anything to read
444 if (size_hint.is_none() || size_hint == Some(0)) && buf.capacity() - buf.len() < PROBE_SIZE {
445 let read = small_probe_read(r, buf)?;
446
447 if read == 0 {
448 return Ok(0);
449 }
450 }
451
452 let mut consecutive_short_reads = 0;
453
454 loop {
455 if buf.len() == buf.capacity() && buf.capacity() == start_cap {
456 // The buffer might be an exact fit. Let's read into a probe buffer
457 // and see if it returns `Ok(0)`. If so, we've avoided an
458 // unnecessary doubling of the capacity. But if not, append the
459 // probe buffer to the primary buffer and let its capacity grow.
460 let read = small_probe_read(r, buf)?;
461
462 if read == 0 {
463 return Ok(buf.len() - start_len);
464 }
465 }
466
467 if buf.len() == buf.capacity() {
468 // buf is full, need more space
469 buf.try_reserve(PROBE_SIZE)?;
470 }
471
472 let mut spare = buf.spare_capacity_mut();
473 let buf_len = cmp::min(spare.len(), max_read_size);
474 spare = &mut spare[..buf_len];
475 let mut read_buf: BorrowedBuf<'_> = spare.into();
476
477 // SAFETY: These bytes were initialized but not filled in the previous loop
478 unsafe {
479 read_buf.set_init(initialized);
480 }
481
482 let mut cursor = read_buf.unfilled();
483 let result = loop {
484 match r.read_buf(cursor.reborrow()) {
485 Err(e) if e.is_interrupted() => continue,
486 // Do not stop now in case of error: we might have received both data
487 // and an error
488 res => break res,
489 }
490 };
491
492 let unfilled_but_initialized = cursor.init_ref().len();
493 let bytes_read = cursor.written();
494 let was_fully_initialized = read_buf.init_len() == buf_len;
495
496 // SAFETY: BorrowedBuf's invariants mean this much memory is initialized.
497 unsafe {
498 let new_len = bytes_read + buf.len();
499 buf.set_len(new_len);
500 }
501
502 // Now that all data is pushed to the vector, we can fail without data loss
503 result?;
504
505 if bytes_read == 0 {
506 return Ok(buf.len() - start_len);
507 }
508
509 if bytes_read < buf_len {
510 consecutive_short_reads += 1;
511 } else {
512 consecutive_short_reads = 0;
513 }
514
515 // store how much was initialized but not filled
516 initialized = unfilled_but_initialized;
517
518 // Use heuristics to determine the max read size if no initial size hint was provided
519 if size_hint.is_none() {
520 // The reader is returning short reads but it doesn't call ensure_init().
521 // In that case we no longer need to restrict read sizes to avoid
522 // initialization costs.
523 // When reading from disk we usually don't get any short reads except at EOF.
524 // So we wait for at least 2 short reads before uncapping the read buffer;
525 // this helps with the Windows issue.
526 if !was_fully_initialized && consecutive_short_reads > 1 {
527 max_read_size = usize::MAX;
528 }
529
530 // we have passed a larger buffer than previously and the
531 // reader still hasn't returned a short read
532 if buf_len >= max_read_size && bytes_read == buf_len {
533 max_read_size = max_read_size.saturating_mul(2);
534 }
535 }
536 }
537}
538
539pub(crate) fn default_read_to_string<R: Read + ?Sized>(
540 r: &mut R,
541 buf: &mut String,
542 size_hint: Option<usize>,
543) -> Result<usize> {
544 // Note that we do *not* call `r.read_to_end()` here. We are passing
545 // `&mut Vec<u8>` (the raw contents of `buf`) into the `read_to_end`
546 // method to fill it up. An arbitrary implementation could overwrite the
547 // entire contents of the vector, not just append to it (which is what
548 // we are expecting).
549 //
550 // To prevent extraneously checking the UTF-8-ness of the entire buffer
551 // we pass it to our hardcoded `default_read_to_end` implementation which
552 // we know is guaranteed to only read data into the end of the buffer.
553 unsafe { append_to_string(buf, |b| default_read_to_end(r, b, size_hint)) }
554}
555
556pub(crate) fn default_read_vectored<F>(read: F, bufs: &mut [IoSliceMut<'_>]) -> Result<usize>
557where
558 F: FnOnce(&mut [u8]) -> Result<usize>,
559{
560 let buf = bufs.iter_mut().find(|b| !b.is_empty()).map_or(&mut [][..], |b| &mut **b);
561 read(buf)
562}
563
564pub(crate) fn default_write_vectored<F>(write: F, bufs: &[IoSlice<'_>]) -> Result<usize>
565where
566 F: FnOnce(&[u8]) -> Result<usize>,
567{
568 let buf = bufs.iter().find(|b| !b.is_empty()).map_or(&[][..], |b| &**b);
569 write(buf)
570}
571
572pub(crate) fn default_read_exact<R: Read + ?Sized>(this: &mut R, mut buf: &mut [u8]) -> Result<()> {
573 while !buf.is_empty() {
574 match this.read(buf) {
575 Ok(0) => break,
576 Ok(n) => {
577 buf = &mut buf[n..];
578 }
579 Err(ref e) if e.is_interrupted() => {}
580 Err(e) => return Err(e),
581 }
582 }
583 if !buf.is_empty() { Err(Error::READ_EXACT_EOF) } else { Ok(()) }
584}
585
586pub(crate) fn default_read_buf<F>(read: F, mut cursor: BorrowedCursor<'_>) -> Result<()>
587where
588 F: FnOnce(&mut [u8]) -> Result<usize>,
589{
590 let n = read(cursor.ensure_init().init_mut())?;
591 cursor.advance(n);
592 Ok(())
593}
594
595pub(crate) fn default_read_buf_exact<R: Read + ?Sized>(
596 this: &mut R,
597 mut cursor: BorrowedCursor<'_>,
598) -> Result<()> {
599 while cursor.capacity() > 0 {
600 let prev_written = cursor.written();
601 match this.read_buf(cursor.reborrow()) {
602 Ok(()) => {}
603 Err(e) if e.is_interrupted() => continue,
604 Err(e) => return Err(e),
605 }
606
607 if cursor.written() == prev_written {
608 return Err(Error::READ_EXACT_EOF);
609 }
610 }
611
612 Ok(())
613}
614
615pub(crate) fn default_write_fmt<W: Write + ?Sized>(
616 this: &mut W,
617 args: fmt::Arguments<'_>,
618) -> Result<()> {
619 // Create a shim which translates a `Write` to a `fmt::Write` and saves off
620 // I/O errors, instead of discarding them.
621 struct Adapter<'a, T: ?Sized + 'a> {
622 inner: &'a mut T,
623 error: Result<()>,
624 }
625
626 impl<T: Write + ?Sized> fmt::Write for Adapter<'_, T> {
627 fn write_str(&mut self, s: &str) -> fmt::Result {
628 match self.inner.write_all(s.as_bytes()) {
629 Ok(()) => Ok(()),
630 Err(e) => {
631 self.error = Err(e);
632 Err(fmt::Error)
633 }
634 }
635 }
636 }
637
638 let mut output = Adapter { inner: this, error: Ok(()) };
639 match fmt::write(&mut output, args) {
640 Ok(()) => Ok(()),
641 Err(..) => {
642 // Check whether the error came from the underlying `Write`.
643 if output.error.is_err() {
644 output.error
645 } else {
646 // This shouldn't happen: the underlying stream did not error,
647 // but somehow the formatter still errored?
648 panic!(
649 "a formatting trait implementation returned an error when the underlying stream did not"
650 );
651 }
652 }
653 }
654}
655
656/// The `Read` trait allows for reading bytes from a source.
657///
658/// Implementors of the `Read` trait are called 'readers'.
659///
660/// Readers are defined by one required method, [`read()`]. Each call to [`read()`]
661/// will attempt to pull bytes from this source into a provided buffer. A
662/// number of other methods are implemented in terms of [`read()`], giving
663/// implementors a number of ways to read bytes while only needing to implement
664/// a single method.
665///
666/// Readers are intended to be composable with one another. Many implementors
667/// throughout [`std::io`] take and provide types which implement the `Read`
668/// trait.
669///
670/// Please note that each call to [`read()`] may involve a system call, and
671/// therefore, using something that implements [`BufRead`], such as
672/// [`BufReader`], will be more efficient.
673///
674/// Repeated calls to the reader use the same cursor, so for example
675/// calling `read_to_end` twice on a [`File`] will only return the file's
676/// contents once. It's recommended to first call `rewind()` in that case.
677///
678/// # Examples
679///
680/// [`File`]s implement `Read`:
681///
682/// ```no_run
683/// use std::io;
684/// use std::io::prelude::*;
685/// use std::fs::File;
686///
687/// fn main() -> io::Result<()> {
688/// let mut f = File::open("foo.txt")?;
689/// let mut buffer = [0; 10];
690///
691/// // read up to 10 bytes
692/// f.read(&mut buffer)?;
693///
694/// let mut buffer = Vec::new();
695/// // read the whole file
696/// f.read_to_end(&mut buffer)?;
697///
698/// // read into a String, so that you don't need to do the conversion.
699/// let mut buffer = String::new();
700/// f.read_to_string(&mut buffer)?;
701///
702/// // and more! See the other methods for more details.
703/// Ok(())
704/// }
705/// ```
706///
707/// Read from [`&str`] because [`&[u8]`][prim@slice] implements `Read`:
708///
709/// ```no_run
710/// # use std::io;
711/// use std::io::prelude::*;
712///
713/// fn main() -> io::Result<()> {
714/// let mut b = "This string will be read".as_bytes();
715/// let mut buffer = [0; 10];
716///
717/// // read up to 10 bytes
718/// b.read(&mut buffer)?;
719///
720/// // etc... it works exactly as a File does!
721/// Ok(())
722/// }
723/// ```
724///
725/// [`read()`]: Read::read
726/// [`&str`]: prim@str
727/// [`std::io`]: self
728/// [`File`]: crate::fs::File
729#[stable(feature = "rust1", since = "1.0.0")]
730#[doc(notable_trait)]
731#[cfg_attr(not(test), rustc_diagnostic_item = "IoRead")]
732pub trait Read {
733 /// Pull some bytes from this source into the specified buffer, returning
734 /// how many bytes were read.
735 ///
736 /// This function does not provide any guarantees about whether it blocks
737 /// waiting for data, but if an object needs to block for a read and cannot,
738 /// it will typically signal this via an [`Err`] return value.
739 ///
740 /// If the return value of this method is [`Ok(n)`], then implementations must
741 /// guarantee that `0 <= n <= buf.len()`. A nonzero `n` value indicates
742 /// that the buffer `buf` has been filled in with `n` bytes of data from this
743 /// source. If `n` is `0`, then it can indicate one of two scenarios:
744 ///
745 /// 1. This reader has reached its "end of file" and will likely no longer
746 /// be able to produce bytes. Note that this does not mean that the
747 /// reader will *always* no longer be able to produce bytes. As an example,
748 /// on Linux, this method will call the `recv` syscall for a [`TcpStream`],
749 /// where returning zero indicates the connection was shut down correctly. While
750 /// for [`File`], it is possible to reach the end of file and get zero as result,
751 /// but if more data is appended to the file, future calls to `read` will return
752 /// more data.
753 /// 2. The buffer specified was 0 bytes in length.
754 ///
755 /// It is not an error if the returned value `n` is smaller than the buffer size,
756 /// even when the reader is not at the end of the stream yet.
757 /// This may happen for example because fewer bytes are actually available right now
758 /// (e. g. being close to end-of-file) or because read() was interrupted by a signal.
759 ///
760 /// As this trait is safe to implement, callers in unsafe code cannot rely on
761 /// `n <= buf.len()` for safety.
762 /// Extra care needs to be taken when `unsafe` functions are used to access the read bytes.
763 /// Callers have to ensure that no unchecked out-of-bounds accesses are possible even if
764 /// `n > buf.len()`.
765 ///
766 /// *Implementations* of this method can make no assumptions about the contents of `buf` when
767 /// this function is called. It is recommended that implementations only write data to `buf`
768 /// instead of reading its contents.
769 ///
770 /// Correspondingly, however, *callers* of this method in unsafe code must not assume
771 /// any guarantees about how the implementation uses `buf`. The trait is safe to implement,
772 /// so it is possible that the code that's supposed to write to the buffer might also read
773 /// from it. It is your responsibility to make sure that `buf` is initialized
774 /// before calling `read`. Calling `read` with an uninitialized `buf` (of the kind one
775 /// obtains via [`MaybeUninit<T>`]) is not safe, and can lead to undefined behavior.
776 ///
777 /// [`MaybeUninit<T>`]: crate::mem::MaybeUninit
778 ///
779 /// # Errors
780 ///
781 /// If this function encounters any form of I/O or other error, an error
782 /// variant will be returned. If an error is returned then it must be
783 /// guaranteed that no bytes were read.
784 ///
785 /// An error of the [`ErrorKind::Interrupted`] kind is non-fatal and the read
786 /// operation should be retried if there is nothing else to do.
787 ///
788 /// # Examples
789 ///
790 /// [`File`]s implement `Read`:
791 ///
792 /// [`Ok(n)`]: Ok
793 /// [`File`]: crate::fs::File
794 /// [`TcpStream`]: crate:🥅:TcpStream
795 ///
796 /// ```no_run
797 /// use std::io;
798 /// use std::io::prelude::*;
799 /// use std::fs::File;
800 ///
801 /// fn main() -> io::Result<()> {
802 /// let mut f = File::open("foo.txt")?;
803 /// let mut buffer = [0; 10];
804 ///
805 /// // read up to 10 bytes
806 /// let n = f.read(&mut buffer[..])?;
807 ///
808 /// println!("The bytes: {:?}", &buffer[..n]);
809 /// Ok(())
810 /// }
811 /// ```
812 #[stable(feature = "rust1", since = "1.0.0")]
813 fn read(&mut self, buf: &mut [u8]) -> Result<usize>;
814
815 /// Like `read`, except that it reads into a slice of buffers.
816 ///
817 /// Data is copied to fill each buffer in order, with the final buffer
818 /// written to possibly being only partially filled. This method must
819 /// behave equivalently to a single call to `read` with concatenated
820 /// buffers.
821 ///
822 /// The default implementation calls `read` with either the first nonempty
823 /// buffer provided, or an empty one if none exists.
824 #[stable(feature = "iovec", since = "1.36.0")]
825 fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> Result<usize> {
826 default_read_vectored(|b| self.read(b), bufs)
827 }
828
829 /// Determines if this `Read`er has an efficient `read_vectored`
830 /// implementation.
831 ///
832 /// If a `Read`er does not override the default `read_vectored`
833 /// implementation, code using it may want to avoid the method all together
834 /// and coalesce writes into a single buffer for higher performance.
835 ///
836 /// The default implementation returns `false`.
837 #[unstable(feature = "can_vector", issue = "69941")]
838 fn is_read_vectored(&self) -> bool {
839 false
840 }
841
842 /// Reads all bytes until EOF in this source, placing them into `buf`.
843 ///
844 /// All bytes read from this source will be appended to the specified buffer
845 /// `buf`. This function will continuously call [`read()`] to append more data to
846 /// `buf` until [`read()`] returns either [`Ok(0)`] or an error of
847 /// non-[`ErrorKind::Interrupted`] kind.
848 ///
849 /// If successful, this function will return the total number of bytes read.
850 ///
851 /// # Errors
852 ///
853 /// If this function encounters an error of the kind
854 /// [`ErrorKind::Interrupted`] then the error is ignored and the operation
855 /// will continue.
856 ///
857 /// If any other read error is encountered then this function immediately
858 /// returns. Any bytes which have already been read will be appended to
859 /// `buf`.
860 ///
861 /// # Examples
862 ///
863 /// [`File`]s implement `Read`:
864 ///
865 /// [`read()`]: Read::read
866 /// [`Ok(0)`]: Ok
867 /// [`File`]: crate::fs::File
868 ///
869 /// ```no_run
870 /// use std::io;
871 /// use std::io::prelude::*;
872 /// use std::fs::File;
873 ///
874 /// fn main() -> io::Result<()> {
875 /// let mut f = File::open("foo.txt")?;
876 /// let mut buffer = Vec::new();
877 ///
878 /// // read the whole file
879 /// f.read_to_end(&mut buffer)?;
880 /// Ok(())
881 /// }
882 /// ```
883 ///
884 /// (See also the [`std::fs::read`] convenience function for reading from a
885 /// file.)
886 ///
887 /// [`std::fs::read`]: crate::fs::read
888 ///
889 /// ## Implementing `read_to_end`
890 ///
891 /// When implementing the `io::Read` trait, it is recommended to allocate
892 /// memory using [`Vec::try_reserve`]. However, this behavior is not guaranteed
893 /// by all implementations, and `read_to_end` may not handle out-of-memory
894 /// situations gracefully.
895 ///
896 /// ```no_run
897 /// # use std::io::{self, BufRead};
898 /// # struct Example { example_datasource: io::Empty } impl Example {
899 /// # fn get_some_data_for_the_example(&self) -> &'static [u8] { &[] }
900 /// fn read_to_end(&mut self, dest_vec: &mut Vec<u8>) -> io::Result<usize> {
901 /// let initial_vec_len = dest_vec.len();
902 /// loop {
903 /// let src_buf = self.example_datasource.fill_buf()?;
904 /// if src_buf.is_empty() {
905 /// break;
906 /// }
907 /// dest_vec.try_reserve(src_buf.len())?;
908 /// dest_vec.extend_from_slice(src_buf);
909 ///
910 /// // Any irreversible side effects should happen after `try_reserve` succeeds,
911 /// // to avoid losing data on allocation error.
912 /// let read = src_buf.len();
913 /// self.example_datasource.consume(read);
914 /// }
915 /// Ok(dest_vec.len() - initial_vec_len)
916 /// }
917 /// # }
918 /// ```
919 ///
920 /// # Usage Notes
921 ///
922 /// `read_to_end` attempts to read a source until EOF, but many sources are continuous streams
923 /// that do not send EOF. In these cases, `read_to_end` will block indefinitely. Standard input
924 /// is one such stream which may be finite if piped, but is typically continuous. For example,
925 /// `cat file | my-rust-program` will correctly terminate with an `EOF` upon closure of cat.
926 /// Reading user input or running programs that remain open indefinitely will never terminate
927 /// the stream with `EOF` (e.g. `yes | my-rust-program`).
928 ///
929 /// Using `.lines()` with a [`BufReader`] or using [`read`] can provide a better solution
930 ///
931 ///[`read`]: Read::read
932 ///
933 /// [`Vec::try_reserve`]: crate::vec::Vec::try_reserve
934 #[stable(feature = "rust1", since = "1.0.0")]
935 fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize> {
936 default_read_to_end(self, buf, None)
937 }
938
939 /// Reads all bytes until EOF in this source, appending them to `buf`.
940 ///
941 /// If successful, this function returns the number of bytes which were read
942 /// and appended to `buf`.
943 ///
944 /// # Errors
945 ///
946 /// If the data in this stream is *not* valid UTF-8 then an error is
947 /// returned and `buf` is unchanged.
948 ///
949 /// See [`read_to_end`] for other error semantics.
950 ///
951 /// [`read_to_end`]: Read::read_to_end
952 ///
953 /// # Examples
954 ///
955 /// [`File`]s implement `Read`:
956 ///
957 /// [`File`]: crate::fs::File
958 ///
959 /// ```no_run
960 /// use std::io;
961 /// use std::io::prelude::*;
962 /// use std::fs::File;
963 ///
964 /// fn main() -> io::Result<()> {
965 /// let mut f = File::open("foo.txt")?;
966 /// let mut buffer = String::new();
967 ///
968 /// f.read_to_string(&mut buffer)?;
969 /// Ok(())
970 /// }
971 /// ```
972 ///
973 /// (See also the [`std::fs::read_to_string`] convenience function for
974 /// reading from a file.)
975 ///
976 /// # Usage Notes
977 ///
978 /// `read_to_string` attempts to read a source until EOF, but many sources are continuous streams
979 /// that do not send EOF. In these cases, `read_to_string` will block indefinitely. Standard input
980 /// is one such stream which may be finite if piped, but is typically continuous. For example,
981 /// `cat file | my-rust-program` will correctly terminate with an `EOF` upon closure of cat.
982 /// Reading user input or running programs that remain open indefinitely will never terminate
983 /// the stream with `EOF` (e.g. `yes | my-rust-program`).
984 ///
985 /// Using `.lines()` with a [`BufReader`] or using [`read`] can provide a better solution
986 ///
987 ///[`read`]: Read::read
988 ///
989 /// [`std::fs::read_to_string`]: crate::fs::read_to_string
990 #[stable(feature = "rust1", since = "1.0.0")]
991 fn read_to_string(&mut self, buf: &mut String) -> Result<usize> {
992 default_read_to_string(self, buf, None)
993 }
994
995 /// Reads the exact number of bytes required to fill `buf`.
996 ///
997 /// This function reads as many bytes as necessary to completely fill the
998 /// specified buffer `buf`.
999 ///
1000 /// *Implementations* of this method can make no assumptions about the contents of `buf` when
1001 /// this function is called. It is recommended that implementations only write data to `buf`
1002 /// instead of reading its contents. The documentation on [`read`] has a more detailed
1003 /// explanation of this subject.
1004 ///
1005 /// # Errors
1006 ///
1007 /// If this function encounters an error of the kind
1008 /// [`ErrorKind::Interrupted`] then the error is ignored and the operation
1009 /// will continue.
1010 ///
1011 /// If this function encounters an "end of file" before completely filling
1012 /// the buffer, it returns an error of the kind [`ErrorKind::UnexpectedEof`].
1013 /// The contents of `buf` are unspecified in this case.
1014 ///
1015 /// If any other read error is encountered then this function immediately
1016 /// returns. The contents of `buf` are unspecified in this case.
1017 ///
1018 /// If this function returns an error, it is unspecified how many bytes it
1019 /// has read, but it will never read more than would be necessary to
1020 /// completely fill the buffer.
1021 ///
1022 /// # Examples
1023 ///
1024 /// [`File`]s implement `Read`:
1025 ///
1026 /// [`read`]: Read::read
1027 /// [`File`]: crate::fs::File
1028 ///
1029 /// ```no_run
1030 /// use std::io;
1031 /// use std::io::prelude::*;
1032 /// use std::fs::File;
1033 ///
1034 /// fn main() -> io::Result<()> {
1035 /// let mut f = File::open("foo.txt")?;
1036 /// let mut buffer = [0; 10];
1037 ///
1038 /// // read exactly 10 bytes
1039 /// f.read_exact(&mut buffer)?;
1040 /// Ok(())
1041 /// }
1042 /// ```
1043 #[stable(feature = "read_exact", since = "1.6.0")]
1044 fn read_exact(&mut self, buf: &mut [u8]) -> Result<()> {
1045 default_read_exact(self, buf)
1046 }
1047
1048 /// Pull some bytes from this source into the specified buffer.
1049 ///
1050 /// This is equivalent to the [`read`](Read::read) method, except that it is passed a [`BorrowedCursor`] rather than `[u8]` to allow use
1051 /// with uninitialized buffers. The new data will be appended to any existing contents of `buf`.
1052 ///
1053 /// The default implementation delegates to `read`.
1054 ///
1055 /// This method makes it possible to return both data and an error but it is advised against.
1056 #[unstable(feature = "read_buf", issue = "78485")]
1057 fn read_buf(&mut self, buf: BorrowedCursor<'_>) -> Result<()> {
1058 default_read_buf(|b| self.read(b), buf)
1059 }
1060
1061 /// Reads the exact number of bytes required to fill `cursor`.
1062 ///
1063 /// This is similar to the [`read_exact`](Read::read_exact) method, except
1064 /// that it is passed a [`BorrowedCursor`] rather than `[u8]` to allow use
1065 /// with uninitialized buffers.
1066 ///
1067 /// # Errors
1068 ///
1069 /// If this function encounters an error of the kind [`ErrorKind::Interrupted`]
1070 /// then the error is ignored and the operation will continue.
1071 ///
1072 /// If this function encounters an "end of file" before completely filling
1073 /// the buffer, it returns an error of the kind [`ErrorKind::UnexpectedEof`].
1074 ///
1075 /// If any other read error is encountered then this function immediately
1076 /// returns.
1077 ///
1078 /// If this function returns an error, all bytes read will be appended to `cursor`.
1079 #[unstable(feature = "read_buf", issue = "78485")]
1080 fn read_buf_exact(&mut self, cursor: BorrowedCursor<'_>) -> Result<()> {
1081 default_read_buf_exact(self, cursor)
1082 }
1083
1084 /// Creates a "by reference" adaptor for this instance of `Read`.
1085 ///
1086 /// The returned adapter also implements `Read` and will simply borrow this
1087 /// current reader.
1088 ///
1089 /// # Examples
1090 ///
1091 /// [`File`]s implement `Read`:
1092 ///
1093 /// [`File`]: crate::fs::File
1094 ///
1095 /// ```no_run
1096 /// use std::io;
1097 /// use std::io::Read;
1098 /// use std::fs::File;
1099 ///
1100 /// fn main() -> io::Result<()> {
1101 /// let mut f = File::open("foo.txt")?;
1102 /// let mut buffer = Vec::new();
1103 /// let mut other_buffer = Vec::new();
1104 ///
1105 /// {
1106 /// let reference = f.by_ref();
1107 ///
1108 /// // read at most 5 bytes
1109 /// reference.take(5).read_to_end(&mut buffer)?;
1110 ///
1111 /// } // drop our &mut reference so we can use f again
1112 ///
1113 /// // original file still usable, read the rest
1114 /// f.read_to_end(&mut other_buffer)?;
1115 /// Ok(())
1116 /// }
1117 /// ```
1118 #[stable(feature = "rust1", since = "1.0.0")]
1119 fn by_ref(&mut self) -> &mut Self
1120 where
1121 Self: Sized,
1122 {
1123 self
1124 }
1125
1126 /// Transforms this `Read` instance to an [`Iterator`] over its bytes.
1127 ///
1128 /// The returned type implements [`Iterator`] where the [`Item`] is
1129 /// <code>[Result]<[u8], [io::Error]></code>.
1130 /// The yielded item is [`Ok`] if a byte was successfully read and [`Err`]
1131 /// otherwise. EOF is mapped to returning [`None`] from this iterator.
1132 ///
1133 /// The default implementation calls `read` for each byte,
1134 /// which can be very inefficient for data that's not in memory,
1135 /// such as [`File`]. Consider using a [`BufReader`] in such cases.
1136 ///
1137 /// # Examples
1138 ///
1139 /// [`File`]s implement `Read`:
1140 ///
1141 /// [`Item`]: Iterator::Item
1142 /// [`File`]: crate::fs::File "fs::File"
1143 /// [Result]: crate::result::Result "Result"
1144 /// [io::Error]: self::Error "io::Error"
1145 ///
1146 /// ```no_run
1147 /// use std::io;
1148 /// use std::io::prelude::*;
1149 /// use std::io::BufReader;
1150 /// use std::fs::File;
1151 ///
1152 /// fn main() -> io::Result<()> {
1153 /// let f = BufReader::new(File::open("foo.txt")?);
1154 ///
1155 /// for byte in f.bytes() {
1156 /// println!("{}", byte?);
1157 /// }
1158 /// Ok(())
1159 /// }
1160 /// ```
1161 #[stable(feature = "rust1", since = "1.0.0")]
1162 fn bytes(self) -> Bytes<Self>
1163 where
1164 Self: Sized,
1165 {
1166 Bytes { inner: self }
1167 }
1168
1169 /// Creates an adapter which will chain this stream with another.
1170 ///
1171 /// The returned `Read` instance will first read all bytes from this object
1172 /// until EOF is encountered. Afterwards the output is equivalent to the
1173 /// output of `next`.
1174 ///
1175 /// # Examples
1176 ///
1177 /// [`File`]s implement `Read`:
1178 ///
1179 /// [`File`]: crate::fs::File
1180 ///
1181 /// ```no_run
1182 /// use std::io;
1183 /// use std::io::prelude::*;
1184 /// use std::fs::File;
1185 ///
1186 /// fn main() -> io::Result<()> {
1187 /// let f1 = File::open("foo.txt")?;
1188 /// let f2 = File::open("bar.txt")?;
1189 ///
1190 /// let mut handle = f1.chain(f2);
1191 /// let mut buffer = String::new();
1192 ///
1193 /// // read the value into a String. We could use any Read method here,
1194 /// // this is just one example.
1195 /// handle.read_to_string(&mut buffer)?;
1196 /// Ok(())
1197 /// }
1198 /// ```
1199 #[stable(feature = "rust1", since = "1.0.0")]
1200 fn chain<R: Read>(self, next: R) -> Chain<Self, R>
1201 where
1202 Self: Sized,
1203 {
1204 Chain { first: self, second: next, done_first: false }
1205 }
1206
1207 /// Creates an adapter which will read at most `limit` bytes from it.
1208 ///
1209 /// This function returns a new instance of `Read` which will read at most
1210 /// `limit` bytes, after which it will always return EOF ([`Ok(0)`]). Any
1211 /// read errors will not count towards the number of bytes read and future
1212 /// calls to [`read()`] may succeed.
1213 ///
1214 /// # Examples
1215 ///
1216 /// [`File`]s implement `Read`:
1217 ///
1218 /// [`File`]: crate::fs::File
1219 /// [`Ok(0)`]: Ok
1220 /// [`read()`]: Read::read
1221 ///
1222 /// ```no_run
1223 /// use std::io;
1224 /// use std::io::prelude::*;
1225 /// use std::fs::File;
1226 ///
1227 /// fn main() -> io::Result<()> {
1228 /// let f = File::open("foo.txt")?;
1229 /// let mut buffer = [0; 5];
1230 ///
1231 /// // read at most five bytes
1232 /// let mut handle = f.take(5);
1233 ///
1234 /// handle.read(&mut buffer)?;
1235 /// Ok(())
1236 /// }
1237 /// ```
1238 #[stable(feature = "rust1", since = "1.0.0")]
1239 fn take(self, limit: u64) -> Take<Self>
1240 where
1241 Self: Sized,
1242 {
1243 Take { inner: self, len: limit, limit }
1244 }
1245}
1246
1247/// Reads all bytes from a [reader][Read] into a new [`String`].
1248///
1249/// This is a convenience function for [`Read::read_to_string`]. Using this
1250/// function avoids having to create a variable first and provides more type
1251/// safety since you can only get the buffer out if there were no errors. (If you
1252/// use [`Read::read_to_string`] you have to remember to check whether the read
1253/// succeeded because otherwise your buffer will be empty or only partially full.)
1254///
1255/// # Performance
1256///
1257/// The downside of this function's increased ease of use and type safety is
1258/// that it gives you less control over performance. For example, you can't
1259/// pre-allocate memory like you can using [`String::with_capacity`] and
1260/// [`Read::read_to_string`]. Also, you can't re-use the buffer if an error
1261/// occurs while reading.
1262///
1263/// In many cases, this function's performance will be adequate and the ease of use
1264/// and type safety tradeoffs will be worth it. However, there are cases where you
1265/// need more control over performance, and in those cases you should definitely use
1266/// [`Read::read_to_string`] directly.
1267///
1268/// Note that in some special cases, such as when reading files, this function will
1269/// pre-allocate memory based on the size of the input it is reading. In those
1270/// cases, the performance should be as good as if you had used
1271/// [`Read::read_to_string`] with a manually pre-allocated buffer.
1272///
1273/// # Errors
1274///
1275/// This function forces you to handle errors because the output (the `String`)
1276/// is wrapped in a [`Result`]. See [`Read::read_to_string`] for the errors
1277/// that can occur. If any error occurs, you will get an [`Err`], so you
1278/// don't have to worry about your buffer being empty or partially full.
1279///
1280/// # Examples
1281///
1282/// ```no_run
1283/// # use std::io;
1284/// fn main() -> io::Result<()> {
1285/// let stdin = io::read_to_string(io::stdin())?;
1286/// println!("Stdin was:");
1287/// println!("{stdin}");
1288/// Ok(())
1289/// }
1290/// ```
1291///
1292/// # Usage Notes
1293///
1294/// `read_to_string` attempts to read a source until EOF, but many sources are continuous streams
1295/// that do not send EOF. In these cases, `read_to_string` will block indefinitely. Standard input
1296/// is one such stream which may be finite if piped, but is typically continuous. For example,
1297/// `cat file | my-rust-program` will correctly terminate with an `EOF` upon closure of cat.
1298/// Reading user input or running programs that remain open indefinitely will never terminate
1299/// the stream with `EOF` (e.g. `yes | my-rust-program`).
1300///
1301/// Using `.lines()` with a [`BufReader`] or using [`read`] can provide a better solution
1302///
1303///[`read`]: Read::read
1304///
1305#[stable(feature = "io_read_to_string", since = "1.65.0")]
1306pub fn read_to_string<R: Read>(mut reader: R) -> Result<String> {
1307 let mut buf = String::new();
1308 reader.read_to_string(&mut buf)?;
1309 Ok(buf)
1310}
1311
1312/// A buffer type used with `Read::read_vectored`.
1313///
1314/// It is semantically a wrapper around a `&mut [u8]`, but is guaranteed to be
1315/// ABI compatible with the `iovec` type on Unix platforms and `WSABUF` on
1316/// Windows.
1317#[stable(feature = "iovec", since = "1.36.0")]
1318#[repr(transparent)]
1319pub struct IoSliceMut<'a>(sys::io::IoSliceMut<'a>);
1320
1321#[stable(feature = "iovec_send_sync", since = "1.44.0")]
1322unsafe impl<'a> Send for IoSliceMut<'a> {}
1323
1324#[stable(feature = "iovec_send_sync", since = "1.44.0")]
1325unsafe impl<'a> Sync for IoSliceMut<'a> {}
1326
1327#[stable(feature = "iovec", since = "1.36.0")]
1328impl<'a> fmt::Debug for IoSliceMut<'a> {
1329 fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
1330 fmt::Debug::fmt(self.0.as_slice(), fmt)
1331 }
1332}
1333
1334impl<'a> IoSliceMut<'a> {
1335 /// Creates a new `IoSliceMut` wrapping a byte slice.
1336 ///
1337 /// # Panics
1338 ///
1339 /// Panics on Windows if the slice is larger than 4GB.
1340 #[stable(feature = "iovec", since = "1.36.0")]
1341 #[inline]
1342 pub fn new(buf: &'a mut [u8]) -> IoSliceMut<'a> {
1343 IoSliceMut(sys::io::IoSliceMut::new(buf))
1344 }
1345
1346 /// Advance the internal cursor of the slice.
1347 ///
1348 /// Also see [`IoSliceMut::advance_slices`] to advance the cursors of
1349 /// multiple buffers.
1350 ///
1351 /// # Panics
1352 ///
1353 /// Panics when trying to advance beyond the end of the slice.
1354 ///
1355 /// # Examples
1356 ///
1357 /// ```
1358 /// use std::io::IoSliceMut;
1359 /// use std::ops::Deref;
1360 ///
1361 /// let mut data = [1; 8];
1362 /// let mut buf = IoSliceMut::new(&mut data);
1363 ///
1364 /// // Mark 3 bytes as read.
1365 /// buf.advance(3);
1366 /// assert_eq!(buf.deref(), [1; 5].as_ref());
1367 /// ```
1368 #[stable(feature = "io_slice_advance", since = "1.81.0")]
1369 #[inline]
1370 pub fn advance(&mut self, n: usize) {
1371 self.0.advance(n)
1372 }
1373
1374 /// Advance a slice of slices.
1375 ///
1376 /// Shrinks the slice to remove any `IoSliceMut`s that are fully advanced over.
1377 /// If the cursor ends up in the middle of an `IoSliceMut`, it is modified
1378 /// to start at that cursor.
1379 ///
1380 /// For example, if we have a slice of two 8-byte `IoSliceMut`s, and we advance by 10 bytes,
1381 /// the result will only include the second `IoSliceMut`, advanced by 2 bytes.
1382 ///
1383 /// # Panics
1384 ///
1385 /// Panics when trying to advance beyond the end of the slices.
1386 ///
1387 /// # Examples
1388 ///
1389 /// ```
1390 /// use std::io::IoSliceMut;
1391 /// use std::ops::Deref;
1392 ///
1393 /// let mut buf1 = [1; 8];
1394 /// let mut buf2 = [2; 16];
1395 /// let mut buf3 = [3; 8];
1396 /// let mut bufs = &mut [
1397 /// IoSliceMut::new(&mut buf1),
1398 /// IoSliceMut::new(&mut buf2),
1399 /// IoSliceMut::new(&mut buf3),
1400 /// ][..];
1401 ///
1402 /// // Mark 10 bytes as read.
1403 /// IoSliceMut::advance_slices(&mut bufs, 10);
1404 /// assert_eq!(bufs[0].deref(), [2; 14].as_ref());
1405 /// assert_eq!(bufs[1].deref(), [3; 8].as_ref());
1406 /// ```
1407 #[stable(feature = "io_slice_advance", since = "1.81.0")]
1408 #[inline]
1409 pub fn advance_slices(bufs: &mut &mut [IoSliceMut<'a>], n: usize) {
1410 // Number of buffers to remove.
1411 let mut remove = 0;
1412 // Remaining length before reaching n.
1413 let mut left = n;
1414 for buf in bufs.iter() {
1415 if let Some(remainder) = left.checked_sub(buf.len()) {
1416 left = remainder;
1417 remove += 1;
1418 } else {
1419 break;
1420 }
1421 }
1422
1423 *bufs = &mut take(bufs)[remove..];
1424 if bufs.is_empty() {
1425 assert!(left == 0, "advancing io slices beyond their length");
1426 } else {
1427 bufs[0].advance(left);
1428 }
1429 }
1430
1431 /// Get the underlying bytes as a mutable slice with the original lifetime.
1432 ///
1433 /// # Examples
1434 ///
1435 /// ```
1436 /// #![feature(io_slice_as_bytes)]
1437 /// use std::io::IoSliceMut;
1438 ///
1439 /// let mut data = *b"abcdef";
1440 /// let io_slice = IoSliceMut::new(&mut data);
1441 /// io_slice.into_slice()[0] = b'A';
1442 ///
1443 /// assert_eq!(&data, b"Abcdef");
1444 /// ```
1445 #[unstable(feature = "io_slice_as_bytes", issue = "132818")]
1446 pub const fn into_slice(self) -> &'a mut [u8] {
1447 self.0.into_slice()
1448 }
1449}
1450
1451#[stable(feature = "iovec", since = "1.36.0")]
1452impl<'a> Deref for IoSliceMut<'a> {
1453 type Target = [u8];
1454
1455 #[inline]
1456 fn deref(&self) -> &[u8] {
1457 self.0.as_slice()
1458 }
1459}
1460
1461#[stable(feature = "iovec", since = "1.36.0")]
1462impl<'a> DerefMut for IoSliceMut<'a> {
1463 #[inline]
1464 fn deref_mut(&mut self) -> &mut [u8] {
1465 self.0.as_mut_slice()
1466 }
1467}
1468
1469/// A buffer type used with `Write::write_vectored`.
1470///
1471/// It is semantically a wrapper around a `&[u8]`, but is guaranteed to be
1472/// ABI compatible with the `iovec` type on Unix platforms and `WSABUF` on
1473/// Windows.
1474#[stable(feature = "iovec", since = "1.36.0")]
1475#[derive(Copy, Clone)]
1476#[repr(transparent)]
1477pub struct IoSlice<'a>(sys::io::IoSlice<'a>);
1478
1479#[stable(feature = "iovec_send_sync", since = "1.44.0")]
1480unsafe impl<'a> Send for IoSlice<'a> {}
1481
1482#[stable(feature = "iovec_send_sync", since = "1.44.0")]
1483unsafe impl<'a> Sync for IoSlice<'a> {}
1484
1485#[stable(feature = "iovec", since = "1.36.0")]
1486impl<'a> fmt::Debug for IoSlice<'a> {
1487 fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
1488 fmt::Debug::fmt(self.0.as_slice(), fmt)
1489 }
1490}
1491
1492impl<'a> IoSlice<'a> {
1493 /// Creates a new `IoSlice` wrapping a byte slice.
1494 ///
1495 /// # Panics
1496 ///
1497 /// Panics on Windows if the slice is larger than 4GB.
1498 #[stable(feature = "iovec", since = "1.36.0")]
1499 #[must_use]
1500 #[inline]
1501 pub fn new(buf: &'a [u8]) -> IoSlice<'a> {
1502 IoSlice(sys::io::IoSlice::new(buf))
1503 }
1504
1505 /// Advance the internal cursor of the slice.
1506 ///
1507 /// Also see [`IoSlice::advance_slices`] to advance the cursors of multiple
1508 /// buffers.
1509 ///
1510 /// # Panics
1511 ///
1512 /// Panics when trying to advance beyond the end of the slice.
1513 ///
1514 /// # Examples
1515 ///
1516 /// ```
1517 /// use std::io::IoSlice;
1518 /// use std::ops::Deref;
1519 ///
1520 /// let data = [1; 8];
1521 /// let mut buf = IoSlice::new(&data);
1522 ///
1523 /// // Mark 3 bytes as read.
1524 /// buf.advance(3);
1525 /// assert_eq!(buf.deref(), [1; 5].as_ref());
1526 /// ```
1527 #[stable(feature = "io_slice_advance", since = "1.81.0")]
1528 #[inline]
1529 pub fn advance(&mut self, n: usize) {
1530 self.0.advance(n)
1531 }
1532
1533 /// Advance a slice of slices.
1534 ///
1535 /// Shrinks the slice to remove any `IoSlice`s that are fully advanced over.
1536 /// If the cursor ends up in the middle of an `IoSlice`, it is modified
1537 /// to start at that cursor.
1538 ///
1539 /// For example, if we have a slice of two 8-byte `IoSlice`s, and we advance by 10 bytes,
1540 /// the result will only include the second `IoSlice`, advanced by 2 bytes.
1541 ///
1542 /// # Panics
1543 ///
1544 /// Panics when trying to advance beyond the end of the slices.
1545 ///
1546 /// # Examples
1547 ///
1548 /// ```
1549 /// use std::io::IoSlice;
1550 /// use std::ops::Deref;
1551 ///
1552 /// let buf1 = [1; 8];
1553 /// let buf2 = [2; 16];
1554 /// let buf3 = [3; 8];
1555 /// let mut bufs = &mut [
1556 /// IoSlice::new(&buf1),
1557 /// IoSlice::new(&buf2),
1558 /// IoSlice::new(&buf3),
1559 /// ][..];
1560 ///
1561 /// // Mark 10 bytes as written.
1562 /// IoSlice::advance_slices(&mut bufs, 10);
1563 /// assert_eq!(bufs[0].deref(), [2; 14].as_ref());
1564 /// assert_eq!(bufs[1].deref(), [3; 8].as_ref());
1565 #[stable(feature = "io_slice_advance", since = "1.81.0")]
1566 #[inline]
1567 pub fn advance_slices(bufs: &mut &mut [IoSlice<'a>], n: usize) {
1568 // Number of buffers to remove.
1569 let mut remove = 0;
1570 // Remaining length before reaching n. This prevents overflow
1571 // that could happen if the length of slices in `bufs` were instead
1572 // accumulated. Those slice may be aliased and, if they are large
1573 // enough, their added length may overflow a `usize`.
1574 let mut left = n;
1575 for buf in bufs.iter() {
1576 if let Some(remainder) = left.checked_sub(buf.len()) {
1577 left = remainder;
1578 remove += 1;
1579 } else {
1580 break;
1581 }
1582 }
1583
1584 *bufs = &mut take(bufs)[remove..];
1585 if bufs.is_empty() {
1586 assert!(left == 0, "advancing io slices beyond their length");
1587 } else {
1588 bufs[0].advance(left);
1589 }
1590 }
1591
1592 /// Get the underlying bytes as a slice with the original lifetime.
1593 ///
1594 /// This doesn't borrow from `self`, so is less restrictive than calling
1595 /// `.deref()`, which does.
1596 ///
1597 /// # Examples
1598 ///
1599 /// ```
1600 /// #![feature(io_slice_as_bytes)]
1601 /// use std::io::IoSlice;
1602 ///
1603 /// let data = b"abcdef";
1604 ///
1605 /// let mut io_slice = IoSlice::new(data);
1606 /// let tail = &io_slice.as_slice()[3..];
1607 ///
1608 /// // This works because `tail` doesn't borrow `io_slice`
1609 /// io_slice = IoSlice::new(tail);
1610 ///
1611 /// assert_eq!(io_slice.as_slice(), b"def");
1612 /// ```
1613 #[unstable(feature = "io_slice_as_bytes", issue = "132818")]
1614 pub const fn as_slice(self) -> &'a [u8] {
1615 self.0.as_slice()
1616 }
1617}
1618
1619#[stable(feature = "iovec", since = "1.36.0")]
1620impl<'a> Deref for IoSlice<'a> {
1621 type Target = [u8];
1622
1623 #[inline]
1624 fn deref(&self) -> &[u8] {
1625 self.0.as_slice()
1626 }
1627}
1628
1629/// A trait for objects which are byte-oriented sinks.
1630///
1631/// Implementors of the `Write` trait are sometimes called 'writers'.
1632///
1633/// Writers are defined by two required methods, [`write`] and [`flush`]:
1634///
1635/// * The [`write`] method will attempt to write some data into the object,
1636/// returning how many bytes were successfully written.
1637///
1638/// * The [`flush`] method is useful for adapters and explicit buffers
1639/// themselves for ensuring that all buffered data has been pushed out to the
1640/// 'true sink'.
1641///
1642/// Writers are intended to be composable with one another. Many implementors
1643/// throughout [`std::io`] take and provide types which implement the `Write`
1644/// trait.
1645///
1646/// [`write`]: Write::write
1647/// [`flush`]: Write::flush
1648/// [`std::io`]: self
1649///
1650/// # Examples
1651///
1652/// ```no_run
1653/// use std::io::prelude::*;
1654/// use std::fs::File;
1655///
1656/// fn main() -> std::io::Result<()> {
1657/// let data = b"some bytes";
1658///
1659/// let mut pos = 0;
1660/// let mut buffer = File::create("foo.txt")?;
1661///
1662/// while pos < data.len() {
1663/// let bytes_written = buffer.write(&data[pos..])?;
1664/// pos += bytes_written;
1665/// }
1666/// Ok(())
1667/// }
1668/// ```
1669///
1670/// The trait also provides convenience methods like [`write_all`], which calls
1671/// `write` in a loop until its entire input has been written.
1672///
1673/// [`write_all`]: Write::write_all
1674#[stable(feature = "rust1", since = "1.0.0")]
1675#[doc(notable_trait)]
1676#[cfg_attr(not(test), rustc_diagnostic_item = "IoWrite")]
1677pub trait Write {
1678 /// Writes a buffer into this writer, returning how many bytes were written.
1679 ///
1680 /// This function will attempt to write the entire contents of `buf`, but
1681 /// the entire write might not succeed, or the write may also generate an
1682 /// error. Typically, a call to `write` represents one attempt to write to
1683 /// any wrapped object.
1684 ///
1685 /// Calls to `write` are not guaranteed to block waiting for data to be
1686 /// written, and a write which would otherwise block can be indicated through
1687 /// an [`Err`] variant.
1688 ///
1689 /// If this method consumed `n > 0` bytes of `buf` it must return [`Ok(n)`].
1690 /// If the return value is `Ok(n)` then `n` must satisfy `n <= buf.len()`.
1691 /// A return value of `Ok(0)` typically means that the underlying object is
1692 /// no longer able to accept bytes and will likely not be able to in the
1693 /// future as well, or that the buffer provided is empty.
1694 ///
1695 /// # Errors
1696 ///
1697 /// Each call to `write` may generate an I/O error indicating that the
1698 /// operation could not be completed. If an error is returned then no bytes
1699 /// in the buffer were written to this writer.
1700 ///
1701 /// It is **not** considered an error if the entire buffer could not be
1702 /// written to this writer.
1703 ///
1704 /// An error of the [`ErrorKind::Interrupted`] kind is non-fatal and the
1705 /// write operation should be retried if there is nothing else to do.
1706 ///
1707 /// # Examples
1708 ///
1709 /// ```no_run
1710 /// use std::io::prelude::*;
1711 /// use std::fs::File;
1712 ///
1713 /// fn main() -> std::io::Result<()> {
1714 /// let mut buffer = File::create("foo.txt")?;
1715 ///
1716 /// // Writes some prefix of the byte string, not necessarily all of it.
1717 /// buffer.write(b"some bytes")?;
1718 /// Ok(())
1719 /// }
1720 /// ```
1721 ///
1722 /// [`Ok(n)`]: Ok
1723 #[stable(feature = "rust1", since = "1.0.0")]
1724 fn write(&mut self, buf: &[u8]) -> Result<usize>;
1725
1726 /// Like [`write`], except that it writes from a slice of buffers.
1727 ///
1728 /// Data is copied from each buffer in order, with the final buffer
1729 /// read from possibly being only partially consumed. This method must
1730 /// behave as a call to [`write`] with the buffers concatenated would.
1731 ///
1732 /// The default implementation calls [`write`] with either the first nonempty
1733 /// buffer provided, or an empty one if none exists.
1734 ///
1735 /// # Examples
1736 ///
1737 /// ```no_run
1738 /// use std::io::IoSlice;
1739 /// use std::io::prelude::*;
1740 /// use std::fs::File;
1741 ///
1742 /// fn main() -> std::io::Result<()> {
1743 /// let data1 = [1; 8];
1744 /// let data2 = [15; 8];
1745 /// let io_slice1 = IoSlice::new(&data1);
1746 /// let io_slice2 = IoSlice::new(&data2);
1747 ///
1748 /// let mut buffer = File::create("foo.txt")?;
1749 ///
1750 /// // Writes some prefix of the byte string, not necessarily all of it.
1751 /// buffer.write_vectored(&[io_slice1, io_slice2])?;
1752 /// Ok(())
1753 /// }
1754 /// ```
1755 ///
1756 /// [`write`]: Write::write
1757 #[stable(feature = "iovec", since = "1.36.0")]
1758 fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> Result<usize> {
1759 default_write_vectored(|b| self.write(b), bufs)
1760 }
1761
1762 /// Determines if this `Write`r has an efficient [`write_vectored`]
1763 /// implementation.
1764 ///
1765 /// If a `Write`r does not override the default [`write_vectored`]
1766 /// implementation, code using it may want to avoid the method all together
1767 /// and coalesce writes into a single buffer for higher performance.
1768 ///
1769 /// The default implementation returns `false`.
1770 ///
1771 /// [`write_vectored`]: Write::write_vectored
1772 #[unstable(feature = "can_vector", issue = "69941")]
1773 fn is_write_vectored(&self) -> bool {
1774 false
1775 }
1776
1777 /// Flushes this output stream, ensuring that all intermediately buffered
1778 /// contents reach their destination.
1779 ///
1780 /// # Errors
1781 ///
1782 /// It is considered an error if not all bytes could be written due to
1783 /// I/O errors or EOF being reached.
1784 ///
1785 /// # Examples
1786 ///
1787 /// ```no_run
1788 /// use std::io::prelude::*;
1789 /// use std::io::BufWriter;
1790 /// use std::fs::File;
1791 ///
1792 /// fn main() -> std::io::Result<()> {
1793 /// let mut buffer = BufWriter::new(File::create("foo.txt")?);
1794 ///
1795 /// buffer.write_all(b"some bytes")?;
1796 /// buffer.flush()?;
1797 /// Ok(())
1798 /// }
1799 /// ```
1800 #[stable(feature = "rust1", since = "1.0.0")]
1801 fn flush(&mut self) -> Result<()>;
1802
1803 /// Attempts to write an entire buffer into this writer.
1804 ///
1805 /// This method will continuously call [`write`] until there is no more data
1806 /// to be written or an error of non-[`ErrorKind::Interrupted`] kind is
1807 /// returned. This method will not return until the entire buffer has been
1808 /// successfully written or such an error occurs. The first error that is
1809 /// not of [`ErrorKind::Interrupted`] kind generated from this method will be
1810 /// returned.
1811 ///
1812 /// If the buffer contains no data, this will never call [`write`].
1813 ///
1814 /// # Errors
1815 ///
1816 /// This function will return the first error of
1817 /// non-[`ErrorKind::Interrupted`] kind that [`write`] returns.
1818 ///
1819 /// [`write`]: Write::write
1820 ///
1821 /// # Examples
1822 ///
1823 /// ```no_run
1824 /// use std::io::prelude::*;
1825 /// use std::fs::File;
1826 ///
1827 /// fn main() -> std::io::Result<()> {
1828 /// let mut buffer = File::create("foo.txt")?;
1829 ///
1830 /// buffer.write_all(b"some bytes")?;
1831 /// Ok(())
1832 /// }
1833 /// ```
1834 #[stable(feature = "rust1", since = "1.0.0")]
1835 fn write_all(&mut self, mut buf: &[u8]) -> Result<()> {
1836 while !buf.is_empty() {
1837 match self.write(buf) {
1838 Ok(0) => {
1839 return Err(Error::WRITE_ALL_EOF);
1840 }
1841 Ok(n) => buf = &buf[n..],
1842 Err(ref e) if e.is_interrupted() => {}
1843 Err(e) => return Err(e),
1844 }
1845 }
1846 Ok(())
1847 }
1848
1849 /// Attempts to write multiple buffers into this writer.
1850 ///
1851 /// This method will continuously call [`write_vectored`] until there is no
1852 /// more data to be written or an error of non-[`ErrorKind::Interrupted`]
1853 /// kind is returned. This method will not return until all buffers have
1854 /// been successfully written or such an error occurs. The first error that
1855 /// is not of [`ErrorKind::Interrupted`] kind generated from this method
1856 /// will be returned.
1857 ///
1858 /// If the buffer contains no data, this will never call [`write_vectored`].
1859 ///
1860 /// # Notes
1861 ///
1862 /// Unlike [`write_vectored`], this takes a *mutable* reference to
1863 /// a slice of [`IoSlice`]s, not an immutable one. That's because we need to
1864 /// modify the slice to keep track of the bytes already written.
1865 ///
1866 /// Once this function returns, the contents of `bufs` are unspecified, as
1867 /// this depends on how many calls to [`write_vectored`] were necessary. It is
1868 /// best to understand this function as taking ownership of `bufs` and to
1869 /// not use `bufs` afterwards. The underlying buffers, to which the
1870 /// [`IoSlice`]s point (but not the [`IoSlice`]s themselves), are unchanged and
1871 /// can be reused.
1872 ///
1873 /// [`write_vectored`]: Write::write_vectored
1874 ///
1875 /// # Examples
1876 ///
1877 /// ```
1878 /// #![feature(write_all_vectored)]
1879 /// # fn main() -> std::io::Result<()> {
1880 ///
1881 /// use std::io::{Write, IoSlice};
1882 ///
1883 /// let mut writer = Vec::new();
1884 /// let bufs = &mut [
1885 /// IoSlice::new(&[1]),
1886 /// IoSlice::new(&[2, 3]),
1887 /// IoSlice::new(&[4, 5, 6]),
1888 /// ];
1889 ///
1890 /// writer.write_all_vectored(bufs)?;
1891 /// // Note: the contents of `bufs` is now undefined, see the Notes section.
1892 ///
1893 /// assert_eq!(writer, &[1, 2, 3, 4, 5, 6]);
1894 /// # Ok(()) }
1895 /// ```
1896 #[unstable(feature = "write_all_vectored", issue = "70436")]
1897 fn write_all_vectored(&mut self, mut bufs: &mut [IoSlice<'_>]) -> Result<()> {
1898 // Guarantee that bufs is empty if it contains no data,
1899 // to avoid calling write_vectored if there is no data to be written.
1900 IoSlice::advance_slices(&mut bufs, 0);
1901 while !bufs.is_empty() {
1902 match self.write_vectored(bufs) {
1903 Ok(0) => {
1904 return Err(Error::WRITE_ALL_EOF);
1905 }
1906 Ok(n) => IoSlice::advance_slices(&mut bufs, n),
1907 Err(ref e) if e.is_interrupted() => {}
1908 Err(e) => return Err(e),
1909 }
1910 }
1911 Ok(())
1912 }
1913
1914 /// Writes a formatted string into this writer, returning any error
1915 /// encountered.
1916 ///
1917 /// This method is primarily used to interface with the
1918 /// [`format_args!()`] macro, and it is rare that this should
1919 /// explicitly be called. The [`write!()`] macro should be favored to
1920 /// invoke this method instead.
1921 ///
1922 /// This function internally uses the [`write_all`] method on
1923 /// this trait and hence will continuously write data so long as no errors
1924 /// are received. This also means that partial writes are not indicated in
1925 /// this signature.
1926 ///
1927 /// [`write_all`]: Write::write_all
1928 ///
1929 /// # Errors
1930 ///
1931 /// This function will return any I/O error reported while formatting.
1932 ///
1933 /// # Examples
1934 ///
1935 /// ```no_run
1936 /// use std::io::prelude::*;
1937 /// use std::fs::File;
1938 ///
1939 /// fn main() -> std::io::Result<()> {
1940 /// let mut buffer = File::create("foo.txt")?;
1941 ///
1942 /// // this call
1943 /// write!(buffer, "{:.*}", 2, 1.234567)?;
1944 /// // turns into this:
1945 /// buffer.write_fmt(format_args!("{:.*}", 2, 1.234567))?;
1946 /// Ok(())
1947 /// }
1948 /// ```
1949 #[stable(feature = "rust1", since = "1.0.0")]
1950 fn write_fmt(&mut self, args: fmt::Arguments<'_>) -> Result<()> {
1951 if let Some(s) = args.as_statically_known_str() {
1952 self.write_all(s.as_bytes())
1953 } else {
1954 default_write_fmt(self, args)
1955 }
1956 }
1957
1958 /// Creates a "by reference" adapter for this instance of `Write`.
1959 ///
1960 /// The returned adapter also implements `Write` and will simply borrow this
1961 /// current writer.
1962 ///
1963 /// # Examples
1964 ///
1965 /// ```no_run
1966 /// use std::io::Write;
1967 /// use std::fs::File;
1968 ///
1969 /// fn main() -> std::io::Result<()> {
1970 /// let mut buffer = File::create("foo.txt")?;
1971 ///
1972 /// let reference = buffer.by_ref();
1973 ///
1974 /// // we can use reference just like our original buffer
1975 /// reference.write_all(b"some bytes")?;
1976 /// Ok(())
1977 /// }
1978 /// ```
1979 #[stable(feature = "rust1", since = "1.0.0")]
1980 fn by_ref(&mut self) -> &mut Self
1981 where
1982 Self: Sized,
1983 {
1984 self
1985 }
1986}
1987
1988/// The `Seek` trait provides a cursor which can be moved within a stream of
1989/// bytes.
1990///
1991/// The stream typically has a fixed size, allowing seeking relative to either
1992/// end or the current offset.
1993///
1994/// # Examples
1995///
1996/// [`File`]s implement `Seek`:
1997///
1998/// [`File`]: crate::fs::File
1999///
2000/// ```no_run
2001/// use std::io;
2002/// use std::io::prelude::*;
2003/// use std::fs::File;
2004/// use std::io::SeekFrom;
2005///
2006/// fn main() -> io::Result<()> {
2007/// let mut f = File::open("foo.txt")?;
2008///
2009/// // move the cursor 42 bytes from the start of the file
2010/// f.seek(SeekFrom::Start(42))?;
2011/// Ok(())
2012/// }
2013/// ```
2014#[stable(feature = "rust1", since = "1.0.0")]
2015#[cfg_attr(not(test), rustc_diagnostic_item = "IoSeek")]
2016pub trait Seek {
2017 /// Seek to an offset, in bytes, in a stream.
2018 ///
2019 /// A seek beyond the end of a stream is allowed, but behavior is defined
2020 /// by the implementation.
2021 ///
2022 /// If the seek operation completed successfully,
2023 /// this method returns the new position from the start of the stream.
2024 /// That position can be used later with [`SeekFrom::Start`].
2025 ///
2026 /// # Errors
2027 ///
2028 /// Seeking can fail, for example because it might involve flushing a buffer.
2029 ///
2030 /// Seeking to a negative offset is considered an error.
2031 #[stable(feature = "rust1", since = "1.0.0")]
2032 fn seek(&mut self, pos: SeekFrom) -> Result<u64>;
2033
2034 /// Rewind to the beginning of a stream.
2035 ///
2036 /// This is a convenience method, equivalent to `seek(SeekFrom::Start(0))`.
2037 ///
2038 /// # Errors
2039 ///
2040 /// Rewinding can fail, for example because it might involve flushing a buffer.
2041 ///
2042 /// # Example
2043 ///
2044 /// ```no_run
2045 /// use std::io::{Read, Seek, Write};
2046 /// use std::fs::OpenOptions;
2047 ///
2048 /// let mut f = OpenOptions::new()
2049 /// .write(true)
2050 /// .read(true)
2051 /// .create(true)
2052 /// .open("foo.txt")?;
2053 ///
2054 /// let hello = "Hello!\n";
2055 /// write!(f, "{hello}")?;
2056 /// f.rewind()?;
2057 ///
2058 /// let mut buf = String::new();
2059 /// f.read_to_string(&mut buf)?;
2060 /// assert_eq!(&buf, hello);
2061 /// # std::io::Result::Ok(())
2062 /// ```
2063 #[stable(feature = "seek_rewind", since = "1.55.0")]
2064 fn rewind(&mut self) -> Result<()> {
2065 self.seek(SeekFrom::Start(0))?;
2066 Ok(())
2067 }
2068
2069 /// Returns the length of this stream (in bytes).
2070 ///
2071 /// The default implementation uses up to three seek operations. If this
2072 /// method returns successfully, the seek position is unchanged (i.e. the
2073 /// position before calling this method is the same as afterwards).
2074 /// However, if this method returns an error, the seek position is
2075 /// unspecified.
2076 ///
2077 /// If you need to obtain the length of *many* streams and you don't care
2078 /// about the seek position afterwards, you can reduce the number of seek
2079 /// operations by simply calling `seek(SeekFrom::End(0))` and using its
2080 /// return value (it is also the stream length).
2081 ///
2082 /// Note that length of a stream can change over time (for example, when
2083 /// data is appended to a file). So calling this method multiple times does
2084 /// not necessarily return the same length each time.
2085 ///
2086 /// # Example
2087 ///
2088 /// ```no_run
2089 /// #![feature(seek_stream_len)]
2090 /// use std::{
2091 /// io::{self, Seek},
2092 /// fs::File,
2093 /// };
2094 ///
2095 /// fn main() -> io::Result<()> {
2096 /// let mut f = File::open("foo.txt")?;
2097 ///
2098 /// let len = f.stream_len()?;
2099 /// println!("The file is currently {len} bytes long");
2100 /// Ok(())
2101 /// }
2102 /// ```
2103 #[unstable(feature = "seek_stream_len", issue = "59359")]
2104 fn stream_len(&mut self) -> Result<u64> {
2105 stream_len_default(self)
2106 }
2107
2108 /// Returns the current seek position from the start of the stream.
2109 ///
2110 /// This is equivalent to `self.seek(SeekFrom::Current(0))`.
2111 ///
2112 /// # Example
2113 ///
2114 /// ```no_run
2115 /// use std::{
2116 /// io::{self, BufRead, BufReader, Seek},
2117 /// fs::File,
2118 /// };
2119 ///
2120 /// fn main() -> io::Result<()> {
2121 /// let mut f = BufReader::new(File::open("foo.txt")?);
2122 ///
2123 /// let before = f.stream_position()?;
2124 /// f.read_line(&mut String::new())?;
2125 /// let after = f.stream_position()?;
2126 ///
2127 /// println!("The first line was {} bytes long", after - before);
2128 /// Ok(())
2129 /// }
2130 /// ```
2131 #[stable(feature = "seek_convenience", since = "1.51.0")]
2132 fn stream_position(&mut self) -> Result<u64> {
2133 self.seek(SeekFrom::Current(0))
2134 }
2135
2136 /// Seeks relative to the current position.
2137 ///
2138 /// This is equivalent to `self.seek(SeekFrom::Current(offset))` but
2139 /// doesn't return the new position which can allow some implementations
2140 /// such as [`BufReader`] to perform more efficient seeks.
2141 ///
2142 /// # Example
2143 ///
2144 /// ```no_run
2145 /// use std::{
2146 /// io::{self, Seek},
2147 /// fs::File,
2148 /// };
2149 ///
2150 /// fn main() -> io::Result<()> {
2151 /// let mut f = File::open("foo.txt")?;
2152 /// f.seek_relative(10)?;
2153 /// assert_eq!(f.stream_position()?, 10);
2154 /// Ok(())
2155 /// }
2156 /// ```
2157 ///
2158 /// [`BufReader`]: crate::io::BufReader
2159 #[stable(feature = "seek_seek_relative", since = "1.80.0")]
2160 fn seek_relative(&mut self, offset: i64) -> Result<()> {
2161 self.seek(SeekFrom::Current(offset))?;
2162 Ok(())
2163 }
2164}
2165
2166pub(crate) fn stream_len_default<T: Seek + ?Sized>(self_: &mut T) -> Result<u64> {
2167 let old_pos = self_.stream_position()?;
2168 let len = self_.seek(SeekFrom::End(0))?;
2169
2170 // Avoid seeking a third time when we were already at the end of the
2171 // stream. The branch is usually way cheaper than a seek operation.
2172 if old_pos != len {
2173 self_.seek(SeekFrom::Start(old_pos))?;
2174 }
2175
2176 Ok(len)
2177}
2178
2179/// Enumeration of possible methods to seek within an I/O object.
2180///
2181/// It is used by the [`Seek`] trait.
2182#[derive(Copy, PartialEq, Eq, Clone, Debug)]
2183#[stable(feature = "rust1", since = "1.0.0")]
2184#[cfg_attr(not(test), rustc_diagnostic_item = "SeekFrom")]
2185pub enum SeekFrom {
2186 /// Sets the offset to the provided number of bytes.
2187 #[stable(feature = "rust1", since = "1.0.0")]
2188 Start(#[stable(feature = "rust1", since = "1.0.0")] u64),
2189
2190 /// Sets the offset to the size of this object plus the specified number of
2191 /// bytes.
2192 ///
2193 /// It is possible to seek beyond the end of an object, but it's an error to
2194 /// seek before byte 0.
2195 #[stable(feature = "rust1", since = "1.0.0")]
2196 End(#[stable(feature = "rust1", since = "1.0.0")] i64),
2197
2198 /// Sets the offset to the current position plus the specified number of
2199 /// bytes.
2200 ///
2201 /// It is possible to seek beyond the end of an object, but it's an error to
2202 /// seek before byte 0.
2203 #[stable(feature = "rust1", since = "1.0.0")]
2204 Current(#[stable(feature = "rust1", since = "1.0.0")] i64),
2205}
2206
2207fn read_until<R: BufRead + ?Sized>(r: &mut R, delim: u8, buf: &mut Vec<u8>) -> Result<usize> {
2208 let mut read = 0;
2209 loop {
2210 let (done, used) = {
2211 let available = match r.fill_buf() {
2212 Ok(n) => n,
2213 Err(ref e) if e.is_interrupted() => continue,
2214 Err(e) => return Err(e),
2215 };
2216 match memchr::memchr(delim, available) {
2217 Some(i) => {
2218 buf.extend_from_slice(&available[..=i]);
2219 (true, i + 1)
2220 }
2221 None => {
2222 buf.extend_from_slice(available);
2223 (false, available.len())
2224 }
2225 }
2226 };
2227 r.consume(used);
2228 read += used;
2229 if done || used == 0 {
2230 return Ok(read);
2231 }
2232 }
2233}
2234
2235fn skip_until<R: BufRead + ?Sized>(r: &mut R, delim: u8) -> Result<usize> {
2236 let mut read = 0;
2237 loop {
2238 let (done, used) = {
2239 let available = match r.fill_buf() {
2240 Ok(n) => n,
2241 Err(ref e) if e.kind() == ErrorKind::Interrupted => continue,
2242 Err(e) => return Err(e),
2243 };
2244 match memchr::memchr(delim, available) {
2245 Some(i) => (true, i + 1),
2246 None => (false, available.len()),
2247 }
2248 };
2249 r.consume(used);
2250 read += used;
2251 if done || used == 0 {
2252 return Ok(read);
2253 }
2254 }
2255}
2256
2257/// A `BufRead` is a type of `Read`er which has an internal buffer, allowing it
2258/// to perform extra ways of reading.
2259///
2260/// For example, reading line-by-line is inefficient without using a buffer, so
2261/// if you want to read by line, you'll need `BufRead`, which includes a
2262/// [`read_line`] method as well as a [`lines`] iterator.
2263///
2264/// # Examples
2265///
2266/// A locked standard input implements `BufRead`:
2267///
2268/// ```no_run
2269/// use std::io;
2270/// use std::io::prelude::*;
2271///
2272/// let stdin = io::stdin();
2273/// for line in stdin.lock().lines() {
2274/// println!("{}", line?);
2275/// }
2276/// # std::io::Result::Ok(())
2277/// ```
2278///
2279/// If you have something that implements [`Read`], you can use the [`BufReader`
2280/// type][`BufReader`] to turn it into a `BufRead`.
2281///
2282/// For example, [`File`] implements [`Read`], but not `BufRead`.
2283/// [`BufReader`] to the rescue!
2284///
2285/// [`File`]: crate::fs::File
2286/// [`read_line`]: BufRead::read_line
2287/// [`lines`]: BufRead::lines
2288///
2289/// ```no_run
2290/// use std::io::{self, BufReader};
2291/// use std::io::prelude::*;
2292/// use std::fs::File;
2293///
2294/// fn main() -> io::Result<()> {
2295/// let f = File::open("foo.txt")?;
2296/// let f = BufReader::new(f);
2297///
2298/// for line in f.lines() {
2299/// let line = line?;
2300/// println!("{line}");
2301/// }
2302///
2303/// Ok(())
2304/// }
2305/// ```
2306#[stable(feature = "rust1", since = "1.0.0")]
2307#[cfg_attr(not(test), rustc_diagnostic_item = "IoBufRead")]
2308pub trait BufRead: Read {
2309 /// Returns the contents of the internal buffer, filling it with more data, via `Read` methods, if empty.
2310 ///
2311 /// This is a lower-level method and is meant to be used together with [`consume`],
2312 /// which can be used to mark bytes that should not be returned by subsequent calls to `read`.
2313 ///
2314 /// [`consume`]: BufRead::consume
2315 ///
2316 /// Returns an empty buffer when the stream has reached EOF.
2317 ///
2318 /// # Errors
2319 ///
2320 /// This function will return an I/O error if a `Read` method was called, but returned an error.
2321 ///
2322 /// # Examples
2323 ///
2324 /// A locked standard input implements `BufRead`:
2325 ///
2326 /// ```no_run
2327 /// use std::io;
2328 /// use std::io::prelude::*;
2329 ///
2330 /// let stdin = io::stdin();
2331 /// let mut stdin = stdin.lock();
2332 ///
2333 /// let buffer = stdin.fill_buf()?;
2334 ///
2335 /// // work with buffer
2336 /// println!("{buffer:?}");
2337 ///
2338 /// // mark the bytes we worked with as read
2339 /// let length = buffer.len();
2340 /// stdin.consume(length);
2341 /// # std::io::Result::Ok(())
2342 /// ```
2343 #[stable(feature = "rust1", since = "1.0.0")]
2344 fn fill_buf(&mut self) -> Result<&[u8]>;
2345
2346 /// Marks the given `amount` of additional bytes from the internal buffer as having been read.
2347 /// Subsequent calls to `read` only return bytes that have not been marked as read.
2348 ///
2349 /// This is a lower-level method and is meant to be used together with [`fill_buf`],
2350 /// which can be used to fill the internal buffer via `Read` methods.
2351 ///
2352 /// It is a logic error if `amount` exceeds the number of unread bytes in the internal buffer, which is returned by [`fill_buf`].
2353 ///
2354 /// # Examples
2355 ///
2356 /// Since `consume()` is meant to be used with [`fill_buf`],
2357 /// that method's example includes an example of `consume()`.
2358 ///
2359 /// [`fill_buf`]: BufRead::fill_buf
2360 #[stable(feature = "rust1", since = "1.0.0")]
2361 fn consume(&mut self, amount: usize);
2362
2363 /// Checks if there is any data left to be `read`.
2364 ///
2365 /// This function may fill the buffer to check for data,
2366 /// so this function returns `Result<bool>`, not `bool`.
2367 ///
2368 /// The default implementation calls `fill_buf` and checks that the
2369 /// returned slice is empty (which means that there is no data left,
2370 /// since EOF is reached).
2371 ///
2372 /// # Errors
2373 ///
2374 /// This function will return an I/O error if a `Read` method was called, but returned an error.
2375 ///
2376 /// Examples
2377 ///
2378 /// ```
2379 /// #![feature(buf_read_has_data_left)]
2380 /// use std::io;
2381 /// use std::io::prelude::*;
2382 ///
2383 /// let stdin = io::stdin();
2384 /// let mut stdin = stdin.lock();
2385 ///
2386 /// while stdin.has_data_left()? {
2387 /// let mut line = String::new();
2388 /// stdin.read_line(&mut line)?;
2389 /// // work with line
2390 /// println!("{line:?}");
2391 /// }
2392 /// # std::io::Result::Ok(())
2393 /// ```
2394 #[unstable(feature = "buf_read_has_data_left", reason = "recently added", issue = "86423")]
2395 fn has_data_left(&mut self) -> Result<bool> {
2396 self.fill_buf().map(|b| !b.is_empty())
2397 }
2398
2399 /// Reads all bytes into `buf` until the delimiter `byte` or EOF is reached.
2400 ///
2401 /// This function will read bytes from the underlying stream until the
2402 /// delimiter or EOF is found. Once found, all bytes up to, and including,
2403 /// the delimiter (if found) will be appended to `buf`.
2404 ///
2405 /// If successful, this function will return the total number of bytes read.
2406 ///
2407 /// This function is blocking and should be used carefully: it is possible for
2408 /// an attacker to continuously send bytes without ever sending the delimiter
2409 /// or EOF.
2410 ///
2411 /// # Errors
2412 ///
2413 /// This function will ignore all instances of [`ErrorKind::Interrupted`] and
2414 /// will otherwise return any errors returned by [`fill_buf`].
2415 ///
2416 /// If an I/O error is encountered then all bytes read so far will be
2417 /// present in `buf` and its length will have been adjusted appropriately.
2418 ///
2419 /// [`fill_buf`]: BufRead::fill_buf
2420 ///
2421 /// # Examples
2422 ///
2423 /// [`std::io::Cursor`][`Cursor`] is a type that implements `BufRead`. In
2424 /// this example, we use [`Cursor`] to read all the bytes in a byte slice
2425 /// in hyphen delimited segments:
2426 ///
2427 /// ```
2428 /// use std::io::{self, BufRead};
2429 ///
2430 /// let mut cursor = io::Cursor::new(b"lorem-ipsum");
2431 /// let mut buf = vec![];
2432 ///
2433 /// // cursor is at 'l'
2434 /// let num_bytes = cursor.read_until(b'-', &mut buf)
2435 /// .expect("reading from cursor won't fail");
2436 /// assert_eq!(num_bytes, 6);
2437 /// assert_eq!(buf, b"lorem-");
2438 /// buf.clear();
2439 ///
2440 /// // cursor is at 'i'
2441 /// let num_bytes = cursor.read_until(b'-', &mut buf)
2442 /// .expect("reading from cursor won't fail");
2443 /// assert_eq!(num_bytes, 5);
2444 /// assert_eq!(buf, b"ipsum");
2445 /// buf.clear();
2446 ///
2447 /// // cursor is at EOF
2448 /// let num_bytes = cursor.read_until(b'-', &mut buf)
2449 /// .expect("reading from cursor won't fail");
2450 /// assert_eq!(num_bytes, 0);
2451 /// assert_eq!(buf, b"");
2452 /// ```
2453 #[stable(feature = "rust1", since = "1.0.0")]
2454 fn read_until(&mut self, byte: u8, buf: &mut Vec<u8>) -> Result<usize> {
2455 read_until(self, byte, buf)
2456 }
2457
2458 /// Skips all bytes until the delimiter `byte` or EOF is reached.
2459 ///
2460 /// This function will read (and discard) bytes from the underlying stream until the
2461 /// delimiter or EOF is found.
2462 ///
2463 /// If successful, this function will return the total number of bytes read,
2464 /// including the delimiter byte.
2465 ///
2466 /// This is useful for efficiently skipping data such as NUL-terminated strings
2467 /// in binary file formats without buffering.
2468 ///
2469 /// This function is blocking and should be used carefully: it is possible for
2470 /// an attacker to continuously send bytes without ever sending the delimiter
2471 /// or EOF.
2472 ///
2473 /// # Errors
2474 ///
2475 /// This function will ignore all instances of [`ErrorKind::Interrupted`] and
2476 /// will otherwise return any errors returned by [`fill_buf`].
2477 ///
2478 /// If an I/O error is encountered then all bytes read so far will be
2479 /// present in `buf` and its length will have been adjusted appropriately.
2480 ///
2481 /// [`fill_buf`]: BufRead::fill_buf
2482 ///
2483 /// # Examples
2484 ///
2485 /// [`std::io::Cursor`][`Cursor`] is a type that implements `BufRead`. In
2486 /// this example, we use [`Cursor`] to read some NUL-terminated information
2487 /// about Ferris from a binary string, skipping the fun fact:
2488 ///
2489 /// ```
2490 /// use std::io::{self, BufRead};
2491 ///
2492 /// let mut cursor = io::Cursor::new(b"Ferris\0Likes long walks on the beach\0Crustacean\0");
2493 ///
2494 /// // read name
2495 /// let mut name = Vec::new();
2496 /// let num_bytes = cursor.read_until(b'\0', &mut name)
2497 /// .expect("reading from cursor won't fail");
2498 /// assert_eq!(num_bytes, 7);
2499 /// assert_eq!(name, b"Ferris\0");
2500 ///
2501 /// // skip fun fact
2502 /// let num_bytes = cursor.skip_until(b'\0')
2503 /// .expect("reading from cursor won't fail");
2504 /// assert_eq!(num_bytes, 30);
2505 ///
2506 /// // read animal type
2507 /// let mut animal = Vec::new();
2508 /// let num_bytes = cursor.read_until(b'\0', &mut animal)
2509 /// .expect("reading from cursor won't fail");
2510 /// assert_eq!(num_bytes, 11);
2511 /// assert_eq!(animal, b"Crustacean\0");
2512 /// ```
2513 #[stable(feature = "bufread_skip_until", since = "1.83.0")]
2514 fn skip_until(&mut self, byte: u8) -> Result<usize> {
2515 skip_until(self, byte)
2516 }
2517
2518 /// Reads all bytes until a newline (the `0xA` byte) is reached, and append
2519 /// them to the provided `String` buffer.
2520 ///
2521 /// Previous content of the buffer will be preserved. To avoid appending to
2522 /// the buffer, you need to [`clear`] it first.
2523 ///
2524 /// This function will read bytes from the underlying stream until the
2525 /// newline delimiter (the `0xA` byte) or EOF is found. Once found, all bytes
2526 /// up to, and including, the delimiter (if found) will be appended to
2527 /// `buf`.
2528 ///
2529 /// If successful, this function will return the total number of bytes read.
2530 ///
2531 /// If this function returns [`Ok(0)`], the stream has reached EOF.
2532 ///
2533 /// This function is blocking and should be used carefully: it is possible for
2534 /// an attacker to continuously send bytes without ever sending a newline
2535 /// or EOF. You can use [`take`] to limit the maximum number of bytes read.
2536 ///
2537 /// [`Ok(0)`]: Ok
2538 /// [`clear`]: String::clear
2539 /// [`take`]: crate::io::Read::take
2540 ///
2541 /// # Errors
2542 ///
2543 /// This function has the same error semantics as [`read_until`] and will
2544 /// also return an error if the read bytes are not valid UTF-8. If an I/O
2545 /// error is encountered then `buf` may contain some bytes already read in
2546 /// the event that all data read so far was valid UTF-8.
2547 ///
2548 /// [`read_until`]: BufRead::read_until
2549 ///
2550 /// # Examples
2551 ///
2552 /// [`std::io::Cursor`][`Cursor`] is a type that implements `BufRead`. In
2553 /// this example, we use [`Cursor`] to read all the lines in a byte slice:
2554 ///
2555 /// ```
2556 /// use std::io::{self, BufRead};
2557 ///
2558 /// let mut cursor = io::Cursor::new(b"foo\nbar");
2559 /// let mut buf = String::new();
2560 ///
2561 /// // cursor is at 'f'
2562 /// let num_bytes = cursor.read_line(&mut buf)
2563 /// .expect("reading from cursor won't fail");
2564 /// assert_eq!(num_bytes, 4);
2565 /// assert_eq!(buf, "foo\n");
2566 /// buf.clear();
2567 ///
2568 /// // cursor is at 'b'
2569 /// let num_bytes = cursor.read_line(&mut buf)
2570 /// .expect("reading from cursor won't fail");
2571 /// assert_eq!(num_bytes, 3);
2572 /// assert_eq!(buf, "bar");
2573 /// buf.clear();
2574 ///
2575 /// // cursor is at EOF
2576 /// let num_bytes = cursor.read_line(&mut buf)
2577 /// .expect("reading from cursor won't fail");
2578 /// assert_eq!(num_bytes, 0);
2579 /// assert_eq!(buf, "");
2580 /// ```
2581 #[stable(feature = "rust1", since = "1.0.0")]
2582 fn read_line(&mut self, buf: &mut String) -> Result<usize> {
2583 // Note that we are not calling the `.read_until` method here, but
2584 // rather our hardcoded implementation. For more details as to why, see
2585 // the comments in `default_read_to_string`.
2586 unsafe { append_to_string(buf, |b| read_until(self, b'\n', b)) }
2587 }
2588
2589 /// Returns an iterator over the contents of this reader split on the byte
2590 /// `byte`.
2591 ///
2592 /// The iterator returned from this function will return instances of
2593 /// <code>[io::Result]<[Vec]\<u8>></code>. Each vector returned will *not* have
2594 /// the delimiter byte at the end.
2595 ///
2596 /// This function will yield errors whenever [`read_until`] would have
2597 /// also yielded an error.
2598 ///
2599 /// [io::Result]: self::Result "io::Result"
2600 /// [`read_until`]: BufRead::read_until
2601 ///
2602 /// # Examples
2603 ///
2604 /// [`std::io::Cursor`][`Cursor`] is a type that implements `BufRead`. In
2605 /// this example, we use [`Cursor`] to iterate over all hyphen delimited
2606 /// segments in a byte slice
2607 ///
2608 /// ```
2609 /// use std::io::{self, BufRead};
2610 ///
2611 /// let cursor = io::Cursor::new(b"lorem-ipsum-dolor");
2612 ///
2613 /// let mut split_iter = cursor.split(b'-').map(|l| l.unwrap());
2614 /// assert_eq!(split_iter.next(), Some(b"lorem".to_vec()));
2615 /// assert_eq!(split_iter.next(), Some(b"ipsum".to_vec()));
2616 /// assert_eq!(split_iter.next(), Some(b"dolor".to_vec()));
2617 /// assert_eq!(split_iter.next(), None);
2618 /// ```
2619 #[stable(feature = "rust1", since = "1.0.0")]
2620 fn split(self, byte: u8) -> Split<Self>
2621 where
2622 Self: Sized,
2623 {
2624 Split { buf: self, delim: byte }
2625 }
2626
2627 /// Returns an iterator over the lines of this reader.
2628 ///
2629 /// The iterator returned from this function will yield instances of
2630 /// <code>[io::Result]<[String]></code>. Each string returned will *not* have a newline
2631 /// byte (the `0xA` byte) or `CRLF` (`0xD`, `0xA` bytes) at the end.
2632 ///
2633 /// [io::Result]: self::Result "io::Result"
2634 ///
2635 /// # Examples
2636 ///
2637 /// [`std::io::Cursor`][`Cursor`] is a type that implements `BufRead`. In
2638 /// this example, we use [`Cursor`] to iterate over all the lines in a byte
2639 /// slice.
2640 ///
2641 /// ```
2642 /// use std::io::{self, BufRead};
2643 ///
2644 /// let cursor = io::Cursor::new(b"lorem\nipsum\r\ndolor");
2645 ///
2646 /// let mut lines_iter = cursor.lines().map(|l| l.unwrap());
2647 /// assert_eq!(lines_iter.next(), Some(String::from("lorem")));
2648 /// assert_eq!(lines_iter.next(), Some(String::from("ipsum")));
2649 /// assert_eq!(lines_iter.next(), Some(String::from("dolor")));
2650 /// assert_eq!(lines_iter.next(), None);
2651 /// ```
2652 ///
2653 /// # Errors
2654 ///
2655 /// Each line of the iterator has the same error semantics as [`BufRead::read_line`].
2656 #[stable(feature = "rust1", since = "1.0.0")]
2657 fn lines(self) -> Lines<Self>
2658 where
2659 Self: Sized,
2660 {
2661 Lines { buf: self }
2662 }
2663}
2664
2665/// Adapter to chain together two readers.
2666///
2667/// This struct is generally created by calling [`chain`] on a reader.
2668/// Please see the documentation of [`chain`] for more details.
2669///
2670/// [`chain`]: Read::chain
2671#[stable(feature = "rust1", since = "1.0.0")]
2672#[derive(Debug)]
2673pub struct Chain<T, U> {
2674 first: T,
2675 second: U,
2676 done_first: bool,
2677}
2678
2679impl<T, U> Chain<T, U> {
2680 /// Consumes the `Chain`, returning the wrapped readers.
2681 ///
2682 /// # Examples
2683 ///
2684 /// ```no_run
2685 /// use std::io;
2686 /// use std::io::prelude::*;
2687 /// use std::fs::File;
2688 ///
2689 /// fn main() -> io::Result<()> {
2690 /// let mut foo_file = File::open("foo.txt")?;
2691 /// let mut bar_file = File::open("bar.txt")?;
2692 ///
2693 /// let chain = foo_file.chain(bar_file);
2694 /// let (foo_file, bar_file) = chain.into_inner();
2695 /// Ok(())
2696 /// }
2697 /// ```
2698 #[stable(feature = "more_io_inner_methods", since = "1.20.0")]
2699 pub fn into_inner(self) -> (T, U) {
2700 (self.first, self.second)
2701 }
2702
2703 /// Gets references to the underlying readers in this `Chain`.
2704 ///
2705 /// Care should be taken to avoid modifying the internal I/O state of the
2706 /// underlying readers as doing so may corrupt the internal state of this
2707 /// `Chain`.
2708 ///
2709 /// # Examples
2710 ///
2711 /// ```no_run
2712 /// use std::io;
2713 /// use std::io::prelude::*;
2714 /// use std::fs::File;
2715 ///
2716 /// fn main() -> io::Result<()> {
2717 /// let mut foo_file = File::open("foo.txt")?;
2718 /// let mut bar_file = File::open("bar.txt")?;
2719 ///
2720 /// let chain = foo_file.chain(bar_file);
2721 /// let (foo_file, bar_file) = chain.get_ref();
2722 /// Ok(())
2723 /// }
2724 /// ```
2725 #[stable(feature = "more_io_inner_methods", since = "1.20.0")]
2726 pub fn get_ref(&self) -> (&T, &U) {
2727 (&self.first, &self.second)
2728 }
2729
2730 /// Gets mutable references to the underlying readers in this `Chain`.
2731 ///
2732 /// Care should be taken to avoid modifying the internal I/O state of the
2733 /// underlying readers as doing so may corrupt the internal state of this
2734 /// `Chain`.
2735 ///
2736 /// # Examples
2737 ///
2738 /// ```no_run
2739 /// use std::io;
2740 /// use std::io::prelude::*;
2741 /// use std::fs::File;
2742 ///
2743 /// fn main() -> io::Result<()> {
2744 /// let mut foo_file = File::open("foo.txt")?;
2745 /// let mut bar_file = File::open("bar.txt")?;
2746 ///
2747 /// let mut chain = foo_file.chain(bar_file);
2748 /// let (foo_file, bar_file) = chain.get_mut();
2749 /// Ok(())
2750 /// }
2751 /// ```
2752 #[stable(feature = "more_io_inner_methods", since = "1.20.0")]
2753 pub fn get_mut(&mut self) -> (&mut T, &mut U) {
2754 (&mut self.first, &mut self.second)
2755 }
2756}
2757
2758#[stable(feature = "rust1", since = "1.0.0")]
2759impl<T: Read, U: Read> Read for Chain<T, U> {
2760 fn read(&mut self, buf: &mut [u8]) -> Result<usize> {
2761 if !self.done_first {
2762 match self.first.read(buf)? {
2763 0 if !buf.is_empty() => self.done_first = true,
2764 n => return Ok(n),
2765 }
2766 }
2767 self.second.read(buf)
2768 }
2769
2770 fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> Result<usize> {
2771 if !self.done_first {
2772 match self.first.read_vectored(bufs)? {
2773 0 if bufs.iter().any(|b| !b.is_empty()) => self.done_first = true,
2774 n => return Ok(n),
2775 }
2776 }
2777 self.second.read_vectored(bufs)
2778 }
2779
2780 #[inline]
2781 fn is_read_vectored(&self) -> bool {
2782 self.first.is_read_vectored() || self.second.is_read_vectored()
2783 }
2784
2785 fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize> {
2786 let mut read = 0;
2787 if !self.done_first {
2788 read += self.first.read_to_end(buf)?;
2789 self.done_first = true;
2790 }
2791 read += self.second.read_to_end(buf)?;
2792 Ok(read)
2793 }
2794
2795 // We don't override `read_to_string` here because an UTF-8 sequence could
2796 // be split between the two parts of the chain
2797
2798 fn read_buf(&mut self, mut buf: BorrowedCursor<'_>) -> Result<()> {
2799 if buf.capacity() == 0 {
2800 return Ok(());
2801 }
2802
2803 if !self.done_first {
2804 let old_len = buf.written();
2805 self.first.read_buf(buf.reborrow())?;
2806
2807 if buf.written() != old_len {
2808 return Ok(());
2809 } else {
2810 self.done_first = true;
2811 }
2812 }
2813 self.second.read_buf(buf)
2814 }
2815}
2816
2817#[stable(feature = "chain_bufread", since = "1.9.0")]
2818impl<T: BufRead, U: BufRead> BufRead for Chain<T, U> {
2819 fn fill_buf(&mut self) -> Result<&[u8]> {
2820 if !self.done_first {
2821 match self.first.fill_buf()? {
2822 buf if buf.is_empty() => self.done_first = true,
2823 buf => return Ok(buf),
2824 }
2825 }
2826 self.second.fill_buf()
2827 }
2828
2829 fn consume(&mut self, amt: usize) {
2830 if !self.done_first { self.first.consume(amt) } else { self.second.consume(amt) }
2831 }
2832
2833 fn read_until(&mut self, byte: u8, buf: &mut Vec<u8>) -> Result<usize> {
2834 let mut read = 0;
2835 if !self.done_first {
2836 let n = self.first.read_until(byte, buf)?;
2837 read += n;
2838
2839 match buf.last() {
2840 Some(b) if *b == byte && n != 0 => return Ok(read),
2841 _ => self.done_first = true,
2842 }
2843 }
2844 read += self.second.read_until(byte, buf)?;
2845 Ok(read)
2846 }
2847
2848 // We don't override `read_line` here because an UTF-8 sequence could be
2849 // split between the two parts of the chain
2850}
2851
2852impl<T, U> SizeHint for Chain<T, U> {
2853 #[inline]
2854 fn lower_bound(&self) -> usize {
2855 SizeHint::lower_bound(&self.first) + SizeHint::lower_bound(&self.second)
2856 }
2857
2858 #[inline]
2859 fn upper_bound(&self) -> Option<usize> {
2860 match (SizeHint::upper_bound(&self.first), SizeHint::upper_bound(&self.second)) {
2861 (Some(first), Some(second)) => first.checked_add(second),
2862 _ => None,
2863 }
2864 }
2865}
2866
2867/// Reader adapter which limits the bytes read from an underlying reader.
2868///
2869/// This struct is generally created by calling [`take`] on a reader.
2870/// Please see the documentation of [`take`] for more details.
2871///
2872/// [`take`]: Read::take
2873#[stable(feature = "rust1", since = "1.0.0")]
2874#[derive(Debug)]
2875pub struct Take<T> {
2876 inner: T,
2877 len: u64,
2878 limit: u64,
2879}
2880
2881impl<T> Take<T> {
2882 /// Returns the number of bytes that can be read before this instance will
2883 /// return EOF.
2884 ///
2885 /// # Note
2886 ///
2887 /// This instance may reach `EOF` after reading fewer bytes than indicated by
2888 /// this method if the underlying [`Read`] instance reaches EOF.
2889 ///
2890 /// # Examples
2891 ///
2892 /// ```no_run
2893 /// use std::io;
2894 /// use std::io::prelude::*;
2895 /// use std::fs::File;
2896 ///
2897 /// fn main() -> io::Result<()> {
2898 /// let f = File::open("foo.txt")?;
2899 ///
2900 /// // read at most five bytes
2901 /// let handle = f.take(5);
2902 ///
2903 /// println!("limit: {}", handle.limit());
2904 /// Ok(())
2905 /// }
2906 /// ```
2907 #[stable(feature = "rust1", since = "1.0.0")]
2908 pub fn limit(&self) -> u64 {
2909 self.limit
2910 }
2911
2912 /// Returns the number of bytes read so far.
2913 #[unstable(feature = "seek_io_take_position", issue = "97227")]
2914 pub fn position(&self) -> u64 {
2915 self.len - self.limit
2916 }
2917
2918 /// Sets the number of bytes that can be read before this instance will
2919 /// return EOF. This is the same as constructing a new `Take` instance, so
2920 /// the amount of bytes read and the previous limit value don't matter when
2921 /// calling this method.
2922 ///
2923 /// # Examples
2924 ///
2925 /// ```no_run
2926 /// use std::io;
2927 /// use std::io::prelude::*;
2928 /// use std::fs::File;
2929 ///
2930 /// fn main() -> io::Result<()> {
2931 /// let f = File::open("foo.txt")?;
2932 ///
2933 /// // read at most five bytes
2934 /// let mut handle = f.take(5);
2935 /// handle.set_limit(10);
2936 ///
2937 /// assert_eq!(handle.limit(), 10);
2938 /// Ok(())
2939 /// }
2940 /// ```
2941 #[stable(feature = "take_set_limit", since = "1.27.0")]
2942 pub fn set_limit(&mut self, limit: u64) {
2943 self.len = limit;
2944 self.limit = limit;
2945 }
2946
2947 /// Consumes the `Take`, returning the wrapped reader.
2948 ///
2949 /// # Examples
2950 ///
2951 /// ```no_run
2952 /// use std::io;
2953 /// use std::io::prelude::*;
2954 /// use std::fs::File;
2955 ///
2956 /// fn main() -> io::Result<()> {
2957 /// let mut file = File::open("foo.txt")?;
2958 ///
2959 /// let mut buffer = [0; 5];
2960 /// let mut handle = file.take(5);
2961 /// handle.read(&mut buffer)?;
2962 ///
2963 /// let file = handle.into_inner();
2964 /// Ok(())
2965 /// }
2966 /// ```
2967 #[stable(feature = "io_take_into_inner", since = "1.15.0")]
2968 pub fn into_inner(self) -> T {
2969 self.inner
2970 }
2971
2972 /// Gets a reference to the underlying reader.
2973 ///
2974 /// Care should be taken to avoid modifying the internal I/O state of the
2975 /// underlying reader as doing so may corrupt the internal limit of this
2976 /// `Take`.
2977 ///
2978 /// # Examples
2979 ///
2980 /// ```no_run
2981 /// use std::io;
2982 /// use std::io::prelude::*;
2983 /// use std::fs::File;
2984 ///
2985 /// fn main() -> io::Result<()> {
2986 /// let mut file = File::open("foo.txt")?;
2987 ///
2988 /// let mut buffer = [0; 5];
2989 /// let mut handle = file.take(5);
2990 /// handle.read(&mut buffer)?;
2991 ///
2992 /// let file = handle.get_ref();
2993 /// Ok(())
2994 /// }
2995 /// ```
2996 #[stable(feature = "more_io_inner_methods", since = "1.20.0")]
2997 pub fn get_ref(&self) -> &T {
2998 &self.inner
2999 }
3000
3001 /// Gets a mutable reference to the underlying reader.
3002 ///
3003 /// Care should be taken to avoid modifying the internal I/O state of the
3004 /// underlying reader as doing so may corrupt the internal limit of this
3005 /// `Take`.
3006 ///
3007 /// # Examples
3008 ///
3009 /// ```no_run
3010 /// use std::io;
3011 /// use std::io::prelude::*;
3012 /// use std::fs::File;
3013 ///
3014 /// fn main() -> io::Result<()> {
3015 /// let mut file = File::open("foo.txt")?;
3016 ///
3017 /// let mut buffer = [0; 5];
3018 /// let mut handle = file.take(5);
3019 /// handle.read(&mut buffer)?;
3020 ///
3021 /// let file = handle.get_mut();
3022 /// Ok(())
3023 /// }
3024 /// ```
3025 #[stable(feature = "more_io_inner_methods", since = "1.20.0")]
3026 pub fn get_mut(&mut self) -> &mut T {
3027 &mut self.inner
3028 }
3029}
3030
3031#[stable(feature = "rust1", since = "1.0.0")]
3032impl<T: Read> Read for Take<T> {
3033 fn read(&mut self, buf: &mut [u8]) -> Result<usize> {
3034 // Don't call into inner reader at all at EOF because it may still block
3035 if self.limit == 0 {
3036 return Ok(0);
3037 }
3038
3039 let max = cmp::min(buf.len() as u64, self.limit) as usize;
3040 let n = self.inner.read(&mut buf[..max])?;
3041 assert!(n as u64 <= self.limit, "number of read bytes exceeds limit");
3042 self.limit -= n as u64;
3043 Ok(n)
3044 }
3045
3046 fn read_buf(&mut self, mut buf: BorrowedCursor<'_>) -> Result<()> {
3047 // Don't call into inner reader at all at EOF because it may still block
3048 if self.limit == 0 {
3049 return Ok(());
3050 }
3051
3052 if self.limit < buf.capacity() as u64 {
3053 // The condition above guarantees that `self.limit` fits in `usize`.
3054 let limit = self.limit as usize;
3055
3056 let extra_init = cmp::min(limit, buf.init_ref().len());
3057
3058 // SAFETY: no uninit data is written to ibuf
3059 let ibuf = unsafe { &mut buf.as_mut()[..limit] };
3060
3061 let mut sliced_buf: BorrowedBuf<'_> = ibuf.into();
3062
3063 // SAFETY: extra_init bytes of ibuf are known to be initialized
3064 unsafe {
3065 sliced_buf.set_init(extra_init);
3066 }
3067
3068 let mut cursor = sliced_buf.unfilled();
3069 let result = self.inner.read_buf(cursor.reborrow());
3070
3071 let new_init = cursor.init_ref().len();
3072 let filled = sliced_buf.len();
3073
3074 // cursor / sliced_buf / ibuf must drop here
3075
3076 unsafe {
3077 // SAFETY: filled bytes have been filled and therefore initialized
3078 buf.advance_unchecked(filled);
3079 // SAFETY: new_init bytes of buf's unfilled buffer have been initialized
3080 buf.set_init(new_init);
3081 }
3082
3083 self.limit -= filled as u64;
3084
3085 result
3086 } else {
3087 let written = buf.written();
3088 let result = self.inner.read_buf(buf.reborrow());
3089 self.limit -= (buf.written() - written) as u64;
3090 result
3091 }
3092 }
3093}
3094
3095#[stable(feature = "rust1", since = "1.0.0")]
3096impl<T: BufRead> BufRead for Take<T> {
3097 fn fill_buf(&mut self) -> Result<&[u8]> {
3098 // Don't call into inner reader at all at EOF because it may still block
3099 if self.limit == 0 {
3100 return Ok(&[]);
3101 }
3102
3103 let buf = self.inner.fill_buf()?;
3104 let cap = cmp::min(buf.len() as u64, self.limit) as usize;
3105 Ok(&buf[..cap])
3106 }
3107
3108 fn consume(&mut self, amt: usize) {
3109 // Don't let callers reset the limit by passing an overlarge value
3110 let amt = cmp::min(amt as u64, self.limit) as usize;
3111 self.limit -= amt as u64;
3112 self.inner.consume(amt);
3113 }
3114}
3115
3116impl<T> SizeHint for Take<T> {
3117 #[inline]
3118 fn lower_bound(&self) -> usize {
3119 cmp::min(SizeHint::lower_bound(&self.inner) as u64, self.limit) as usize
3120 }
3121
3122 #[inline]
3123 fn upper_bound(&self) -> Option<usize> {
3124 match SizeHint::upper_bound(&self.inner) {
3125 Some(upper_bound) => Some(cmp::min(upper_bound as u64, self.limit) as usize),
3126 None => self.limit.try_into().ok(),
3127 }
3128 }
3129}
3130
3131#[stable(feature = "seek_io_take", since = "CURRENT_RUSTC_VERSION")]
3132impl<T: Seek> Seek for Take<T> {
3133 fn seek(&mut self, pos: SeekFrom) -> Result<u64> {
3134 let new_position = match pos {
3135 SeekFrom::Start(v) => Some(v),
3136 SeekFrom::Current(v) => self.position().checked_add_signed(v),
3137 SeekFrom::End(v) => self.len.checked_add_signed(v),
3138 };
3139 let new_position = match new_position {
3140 Some(v) if v <= self.len => v,
3141 _ => return Err(ErrorKind::InvalidInput.into()),
3142 };
3143 while new_position != self.position() {
3144 if let Some(offset) = new_position.checked_signed_diff(self.position()) {
3145 self.inner.seek_relative(offset)?;
3146 self.limit = self.limit.wrapping_sub(offset as u64);
3147 break;
3148 }
3149 let offset = if new_position > self.position() { i64::MAX } else { i64::MIN };
3150 self.inner.seek_relative(offset)?;
3151 self.limit = self.limit.wrapping_sub(offset as u64);
3152 }
3153 Ok(new_position)
3154 }
3155
3156 fn stream_len(&mut self) -> Result<u64> {
3157 Ok(self.len)
3158 }
3159
3160 fn stream_position(&mut self) -> Result<u64> {
3161 Ok(self.position())
3162 }
3163
3164 fn seek_relative(&mut self, offset: i64) -> Result<()> {
3165 if !self.position().checked_add_signed(offset).is_some_and(|p| p <= self.len) {
3166 return Err(ErrorKind::InvalidInput.into());
3167 }
3168 self.inner.seek_relative(offset)?;
3169 self.limit = self.limit.wrapping_sub(offset as u64);
3170 Ok(())
3171 }
3172}
3173
3174/// An iterator over `u8` values of a reader.
3175///
3176/// This struct is generally created by calling [`bytes`] on a reader.
3177/// Please see the documentation of [`bytes`] for more details.
3178///
3179/// [`bytes`]: Read::bytes
3180#[stable(feature = "rust1", since = "1.0.0")]
3181#[derive(Debug)]
3182pub struct Bytes<R> {
3183 inner: R,
3184}
3185
3186#[stable(feature = "rust1", since = "1.0.0")]
3187impl<R: Read> Iterator for Bytes<R> {
3188 type Item = Result<u8>;
3189
3190 // Not `#[inline]`. This function gets inlined even without it, but having
3191 // the inline annotation can result in worse code generation. See #116785.
3192 fn next(&mut self) -> Option<Result<u8>> {
3193 SpecReadByte::spec_read_byte(&mut self.inner)
3194 }
3195
3196 #[inline]
3197 fn size_hint(&self) -> (usize, Option<usize>) {
3198 SizeHint::size_hint(&self.inner)
3199 }
3200}
3201
3202/// For the specialization of `Bytes::next`.
3203trait SpecReadByte {
3204 fn spec_read_byte(&mut self) -> Option<Result<u8>>;
3205}
3206
3207impl<R> SpecReadByte for R
3208where
3209 Self: Read,
3210{
3211 #[inline]
3212 default fn spec_read_byte(&mut self) -> Option<Result<u8>> {
3213 inlined_slow_read_byte(self)
3214 }
3215}
3216
3217/// Reads a single byte in a slow, generic way. This is used by the default
3218/// `spec_read_byte`.
3219#[inline]
3220fn inlined_slow_read_byte<R: Read>(reader: &mut R) -> Option<Result<u8>> {
3221 let mut byte = 0;
3222 loop {
3223 return match reader.read(slice::from_mut(&mut byte)) {
3224 Ok(0) => None,
3225 Ok(..) => Some(Ok(byte)),
3226 Err(ref e) if e.is_interrupted() => continue,
3227 Err(e) => Some(Err(e)),
3228 };
3229 }
3230}
3231
3232// Used by `BufReader::spec_read_byte`, for which the `inline(ever)` is
3233// important.
3234#[inline(never)]
3235fn uninlined_slow_read_byte<R: Read>(reader: &mut R) -> Option<Result<u8>> {
3236 inlined_slow_read_byte(reader)
3237}
3238
3239trait SizeHint {
3240 fn lower_bound(&self) -> usize;
3241
3242 fn upper_bound(&self) -> Option<usize>;
3243
3244 fn size_hint(&self) -> (usize, Option<usize>) {
3245 (self.lower_bound(), self.upper_bound())
3246 }
3247}
3248
3249impl<T: ?Sized> SizeHint for T {
3250 #[inline]
3251 default fn lower_bound(&self) -> usize {
3252 0
3253 }
3254
3255 #[inline]
3256 default fn upper_bound(&self) -> Option<usize> {
3257 None
3258 }
3259}
3260
3261impl<T> SizeHint for &mut T {
3262 #[inline]
3263 fn lower_bound(&self) -> usize {
3264 SizeHint::lower_bound(*self)
3265 }
3266
3267 #[inline]
3268 fn upper_bound(&self) -> Option<usize> {
3269 SizeHint::upper_bound(*self)
3270 }
3271}
3272
3273impl<T> SizeHint for Box<T> {
3274 #[inline]
3275 fn lower_bound(&self) -> usize {
3276 SizeHint::lower_bound(&**self)
3277 }
3278
3279 #[inline]
3280 fn upper_bound(&self) -> Option<usize> {
3281 SizeHint::upper_bound(&**self)
3282 }
3283}
3284
3285impl SizeHint for &[u8] {
3286 #[inline]
3287 fn lower_bound(&self) -> usize {
3288 self.len()
3289 }
3290
3291 #[inline]
3292 fn upper_bound(&self) -> Option<usize> {
3293 Some(self.len())
3294 }
3295}
3296
3297/// An iterator over the contents of an instance of `BufRead` split on a
3298/// particular byte.
3299///
3300/// This struct is generally created by calling [`split`] on a `BufRead`.
3301/// Please see the documentation of [`split`] for more details.
3302///
3303/// [`split`]: BufRead::split
3304#[stable(feature = "rust1", since = "1.0.0")]
3305#[derive(Debug)]
3306pub struct Split<B> {
3307 buf: B,
3308 delim: u8,
3309}
3310
3311#[stable(feature = "rust1", since = "1.0.0")]
3312impl<B: BufRead> Iterator for Split<B> {
3313 type Item = Result<Vec<u8>>;
3314
3315 fn next(&mut self) -> Option<Result<Vec<u8>>> {
3316 let mut buf = Vec::new();
3317 match self.buf.read_until(self.delim, &mut buf) {
3318 Ok(0) => None,
3319 Ok(_n) => {
3320 if buf[buf.len() - 1] == self.delim {
3321 buf.pop();
3322 }
3323 Some(Ok(buf))
3324 }
3325 Err(e) => Some(Err(e)),
3326 }
3327 }
3328}
3329
3330/// An iterator over the lines of an instance of `BufRead`.
3331///
3332/// This struct is generally created by calling [`lines`] on a `BufRead`.
3333/// Please see the documentation of [`lines`] for more details.
3334///
3335/// [`lines`]: BufRead::lines
3336#[stable(feature = "rust1", since = "1.0.0")]
3337#[derive(Debug)]
3338#[cfg_attr(not(test), rustc_diagnostic_item = "IoLines")]
3339pub struct Lines<B> {
3340 buf: B,
3341}
3342
3343#[stable(feature = "rust1", since = "1.0.0")]
3344impl<B: BufRead> Iterator for Lines<B> {
3345 type Item = Result<String>;
3346
3347 fn next(&mut self) -> Option<Result<String>> {
3348 let mut buf = String::new();
3349 match self.buf.read_line(&mut buf) {
3350 Ok(0) => None,
3351 Ok(_n) => {
3352 if buf.ends_with('\n') {
3353 buf.pop();
3354 if buf.ends_with('\r') {
3355 buf.pop();
3356 }
3357 }
3358 Some(Ok(buf))
3359 }
3360 Err(e) => Some(Err(e)),
3361 }
3362 }
3363}